iavf: Fix NULL pointer dereference in iavf_get_link_ksettings

In the Linux kernel, the following vulnerability has been resolved:

iavf: Fix NULL pointer dereference in iavf_get_link_ksettings

Fix possible NULL pointer dereference, due to freeing of adapter->vf_res
in iavf_init_get_resources. Previous commit introduced a regression,
where receiving IAVF_ERR_ADMIN_QUEUE_NO_WORK from iavf_get_vf_config
would free adapter->vf_res. However, netdev is still registered, so
ethtool_ops can be called. Calling iavf_get_link_ksettings with no vf_res,
will result with:
[ 9385.242676] BUG: kernel NULL pointer dereference, address: 0000000000000008
[ 9385.242683] #PF: supervisor read access in kernel mode
[ 9385.242686] #PF: error_code(0x0000) - not-present page
[ 9385.242690] PGD 0 P4D 0
[ 9385.242696] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI
[ 9385.242701] CPU: 6 PID: 3217 Comm: pmdalinux Kdump: loaded Tainted: G S E 5.18.0-04958-ga54ce3703613-dirty #1
[ 9385.242708] Hardware name: Dell Inc. PowerEdge R730/0WCJNT, BIOS 2.11.0 11/02/2019
[ 9385.242710] RIP: 0010:iavf_get_link_ksettings+0x29/0xd0 [iavf]
[ 9385.242745] Code: 00 0f 1f 44 00 00 b8 01 ef ff ff 48 c7 46 30 00 00 00 00 48 c7 46 38 00 00 00 00 c6 46 0b 00 66 89 46 08 48 8b 87 68 0e 00 00 <f6> 40 08 80 75 50 8b 87 5c 0e 00 00 83 f8 08 74 7a 76 1d 83 f8 20
[ 9385.242749] RSP: 0018:ffffc0560ec7fbd0 EFLAGS: 00010246
[ 9385.242755] RAX: 0000000000000000 RBX: ffffc0560ec7fc08 RCX: 0000000000000000
[ 9385.242759] RDX: ffffffffc0ad4550 RSI: ffffc0560ec7fc08 RDI: ffffa0fc66674000
[ 9385.242762] RBP: 00007ffd1fb2bf50 R08: b6a2d54b892363ee R09: ffffa101dc14fb00
[ 9385.242765] R10: 0000000000000000 R11: 0000000000000004 R12: ffffa0fc66674000
[ 9385.242768] R13: 0000000000000000 R14: ffffa0fc66674000 R15: 00000000ffffffa1
[ 9385.242771] FS: 00007f93711a2980(0000) GS:ffffa0fad72c0000(0000) knlGS:0000000000000000
[ 9385.242775] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 9385.242778] CR2: 0000000000000008 CR3: 0000000a8e61c003 CR4: 00000000003706e0
[ 9385.242781] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 9385.242784] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 9385.242787] Call Trace:
[ 9385.242791] <TASK>
[ 9385.242793] ethtool_get_settings+0x71/0x1a0
[ 9385.242814] __dev_ethtool+0x426/0x2f40
[ 9385.242823] ? slab_post_alloc_hook+0x4f/0x280
[ 9385.242836] ? kmem_cache_alloc_trace+0x15d/0x2f0
[ 9385.242841] ? dev_ethtool+0x59/0x170
[ 9385.242848] dev_ethtool+0xa7/0x170
[ 9385.242856] dev_ioctl+0xc3/0x520
[ 9385.242866] sock_do_ioctl+0xa0/0xe0
[ 9385.242877] sock_ioctl+0x22f/0x320
[ 9385.242885] __x64_sys_ioctl+0x84/0xc0
[ 9385.242896] do_syscall_64+0x3a/0x80
[ 9385.242904] entry_SYSCALL_64_after_hwframe+0x46/0xb0
[ 9385.242918] RIP: 0033:0x7f93702396db
[ 9385.242923] Code: 73 01 c3 48 8b 0d ad 57 38 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 7d 57 38 00 f7 d8 64 89 01 48
[ 9385.242927] RSP: 002b:00007ffd1fb2bf18 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[ 9385.242932] RAX: ffffffffffffffda RBX: 000055671b1d2fe0 RCX: 00007f93702396db
[ 9385.242935] RDX: 00007ffd1fb2bf20 RSI: 0000000000008946 RDI: 0000000000000007
[ 9385.242937] RBP: 00007ffd1fb2bf20 R08: 0000000000000003 R09: 0030763066307330
[ 9385.242940] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd1fb2bf80
[ 9385.242942] R13: 0000000000000007 R14: 0000556719f6de90 R15: 00007ffd1fb2c1b0
[ 9385.242948] </TASK>
[ 9385.242949] Modules linked in: iavf(E) xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nft_compat nf_nat_tftp nft_objref nf_conntrack_tftp bridge stp llc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables rfkill nfnetlink vfat fat irdma ib_uverbs ib_core intel_rapl_msr intel_rapl_common sb_edac x86_pkg_temp_thermal intel_powerclamp coretem
---truncated---