net: ipv4: fix route with nexthop object delete warning

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

net: ipv4: fix route with nexthop object delete warning

FRR folks have hit a kernel warning[1] while deleting routes[2] which is
caused by trying to delete a route pointing to a nexthop id without
specifying nhid but matching on an interface. That is, a route is found
but we hit a warning while matching it. The warning is from
fib_info_nh() in include/net/nexthop.h because we run it on a fib_info
with nexthop object. The call chain is:
inet_rtm_delroute -> fib_table_delete -> fib_nh_match (called with a
nexthop fib_info and also with fc_oif set thus calling fib_info_nh on
the fib_info and triggering the warning). The fix is to not do any
matching in that branch if the fi has a nexthop object because those are
managed separately. I.e. we should match when deleting without nh spec and
should fail when deleting a nexthop route with old-style nh spec because
nexthop objects are managed separately, e.g.:
$ ip r show 1.2.3.4/32
1.2.3.4 nhid 12 via 192.168.11.2 dev dummy0

$ ip r del 1.2.3.4/32
$ ip r del 1.2.3.4/32 nhid 12
<both should work>

$ ip r del 1.2.3.4/32 dev dummy0
<should fail with ESRCH>

[1]
[ 523.462226] ------------[ cut here ]------------
[ 523.462230] WARNING: CPU: 14 PID: 22893 at include/net/nexthop.h:468 fib_nh_match+0x210/0x460
[ 523.462236] Modules linked in: dummy rpcsec_gss_krb5 xt_socket nf_socket_ipv4 nf_socket_ipv6 ip6table_raw iptable_raw bpf_preload xt_statistic ip_set ip_vs_sh ip_vs_wrr ip_vs_rr ip_vs xt_mark nf_tables xt_nat veth nf_conntrack_netlink nfnetlink xt_addrtype br_netfilter overlay dm_crypt nfsv3 nfs fscache netfs vhost_net vhost vhost_iotlb tap tun xt_CHECKSUM xt_MASQUERADE xt_conntrack 8021q garp mrp ipt_REJECT nf_reject_ipv4 ip6table_mangle ip6table_nat iptable_mangle iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_filter bridge stp llc rfcomm snd_seq_dummy snd_hrtimer rpcrdma rdma_cm iw_cm ib_cm ib_core ip6table_filter xt_comment ip6_tables vboxnetadp(OE) vboxnetflt(OE) vboxdrv(OE) qrtr bnep binfmt_misc xfs vfat fat squashfs loop nvidia_drm(POE) nvidia_modeset(POE) nvidia_uvm(POE) nvidia(POE) intel_rapl_msr intel_rapl_common snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio snd_hda_codec_hdmi btusb btrtl iwlmvm uvcvideo btbcm snd_hda_intel edac_mce_amd
[ 523.462274] videobuf2_vmalloc videobuf2_memops btintel snd_intel_dspcfg videobuf2_v4l2 snd_intel_sdw_acpi bluetooth snd_usb_audio snd_hda_codec mac80211 snd_usbmidi_lib joydev snd_hda_core videobuf2_common kvm_amd snd_rawmidi snd_hwdep snd_seq videodev ccp snd_seq_device libarc4 ecdh_generic mc snd_pcm kvm iwlwifi snd_timer drm_kms_helper snd cfg80211 cec soundcore irqbypass rapl wmi_bmof i2c_piix4 rfkill k10temp pcspkr acpi_cpufreq nfsd auth_rpcgss nfs_acl lockd grace sunrpc drm zram ip_tables crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel nvme sp5100_tco r8169 nvme_core wmi ipmi_devintf ipmi_msghandler fuse
[ 523.462300] CPU: 14 PID: 22893 Comm: ip Tainted: P OE 5.16.18-200.fc35.x86_64 #1
[ 523.462302] Hardware name: Micro-Star International Co., Ltd. MS-7C37/MPG X570 GAMING EDGE WIFI (MS-7C37), BIOS 1.C0 10/29/2020
[ 523.462303] RIP: 0010:fib_nh_match+0x210/0x460
[ 523.462304] Code: 7c 24 20 48 8b b5 90 00 00 00 e8 bb ee f4 ff 48 8b 7c 24 20 41 89 c4 e8 ee eb f4 ff 45 85 e4 0f 85 2e fe ff ff e9 4c ff ff ff <0f> 0b e9 17 ff ff ff 3c 0a 0f 85 61 fe ff ff 48 8b b5 98 00 00 00
[ 523.462306] RSP: 0018:ffffaa53d4d87928 EFLAGS: 00010286
[ 523.462307] RAX: 0000000000000000 RBX: ffffaa53d4d87a90 RCX: ffffaa53d4d87bb0
[ 523.462308] RDX: ffff9e3d2ee6be80 RSI: ffffaa53d4d87a90 RDI: ffffffff920ed380
[ 523.462309] RBP: ffff9e3d2ee6be80 R08: 0000000000000064 R09: 0000000000000000
[ 523.462310] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000031
[ 523.462310] R13: 0000000000000020 R14: 0000000000000000 R15: ffff9e3d331054e0
[ 523.462311] FS: 00007f2455
---truncated---