net/mlx5: Unregister notifier on eswitch init failure

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

net/mlx5: Unregister notifier on eswitch init failure

It otherwise remains registered and a subsequent attempt at eswitch

enabling might trigger warnings of the sort:

[ 682.589148] ------------[ cut here ]------------

[ 682.590204] notifier callback eswitch_vport_event [mlx5_core] already registered

[ 682.590256] WARNING: CPU: 13 PID: 2660 at kernel/notifier.c:31 notifier_chain_register+0x3e/0x90

[...snipped]

[ 682.610052] Call Trace:

[ 682.610369] <TASK>

[ 682.610663] ? __warn+0x7c/0x110

[ 682.611050] ? notifier_chain_register+0x3e/0x90

[ 682.611556] ? report_bug+0x148/0x170

[ 682.611977] ? handle_bug+0x36/0x70

[ 682.612384] ? exc_invalid_op+0x13/0x60

[ 682.612817] ? asm_exc_invalid_op+0x16/0x20

[ 682.613284] ? notifier_chain_register+0x3e/0x90

[ 682.613789] atomic_notifier_chain_register+0x25/0x40

[ 682.614322] mlx5_eswitch_enable_locked+0x1d4/0x3b0 [mlx5_core]

[ 682.614965] mlx5_eswitch_enable+0xc9/0x100 [mlx5_core]

[ 682.615551] mlx5_device_enable_sriov+0x25/0x340 [mlx5_core]

[ 682.616170] mlx5_core_sriov_configure+0x50/0x170 [mlx5_core]

[ 682.616789] sriov_numvfs_store+0xb0/0x1b0

[ 682.617248] kernfs_fop_write_iter+0x117/0x1a0

[ 682.617734] vfs_write+0x231/0x3f0

[ 682.618138] ksys_write+0x63/0xe0

[ 682.618536] do_syscall_64+0x4c/0x100

[ 682.618958] entry_SYSCALL_64_after_hwframe+0x4b/0x53