bnxt_en: Fix double invocation of bnxt_ulp_stop()/bnxt_ulp_start()

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

bnxt_en: Fix double invocation of bnxt_ulp_stop()/bnxt_ulp_start()

Before the commit under the Fixes tag below, bnxt_ulp_stop() and
bnxt_ulp_start() were always invoked in pairs. After that commit,
the new bnxt_ulp_restart() can be invoked after bnxt_ulp_stop()
has been called. This may result in the RoCE driver's aux driver
.suspend() method being invoked twice. The 2nd bnxt_re_suspend()
call will crash when it dereferences a NULL pointer:

(NULL ib_device): Handle device suspend call
BUG: kernel NULL pointer dereference, address: 0000000000000b78
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP PTI
CPU: 20 UID: 0 PID: 181 Comm: kworker/u96:5 Tainted: G S 6.15.0-rc1 #4 PREEMPT(voluntary)
Tainted: [S]=CPU_OUT_OF_SPEC
Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017
Workqueue: bnxt_pf_wq bnxt_sp_task [bnxt_en]
RIP: 0010:bnxt_re_suspend+0x45/0x1f0 [bnxt_re]
Code: 8b 05 a7 3c 5b f5 48 89 44 24 18 31 c0 49 8b 5c 24 08 4d 8b 2c 24 e8 ea 06 0a f4 48 c7 c6 04 60 52 c0 48 89 df e8 1b ce f9 ff <48> 8b 83 78 0b 00 00 48 8b 80 38 03 00 00 a8 40 0f 85 b5 00 00 00
RSP: 0018:ffffa2e84084fd88 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffffb4b6b934 RDI: 00000000ffffffff
RBP: ffffa1760954c9c0 R08: 0000000000000000 R09: c0000000ffffdfff
R10: 0000000000000001 R11: ffffa2e84084fb50 R12: ffffa176031ef070
R13: ffffa17609775000 R14: ffffa17603adc180 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffffa17daa397000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000b78 CR3: 00000004aaa30003 CR4: 00000000003706f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
bnxt_ulp_stop+0x69/0x90 [bnxt_en]
bnxt_sp_task+0x678/0x920 [bnxt_en]
? __schedule+0x514/0xf50
process_scheduled_works+0x9d/0x400
worker_thread+0x11c/0x260
? __pfx_worker_thread+0x10/0x10
kthread+0xfe/0x1e0
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2b/0x40
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30

Check the BNXT_EN_FLAG_ULP_STOPPED flag and do not proceed if the flag
is already set. This will preserve the original symmetrical
bnxt_ulp_stop() and bnxt_ulp_start().

Also, inside bnxt_ulp_start(), clear the BNXT_EN_FLAG_ULP_STOPPED
flag after taking the mutex to avoid any race condition. And for
symmetry, only proceed in bnxt_ulp_start() if the
BNXT_EN_FLAG_ULP_STOPPED is set.