Fixed the system panic during EEH recovery (CR 127062)

Fixed the system panic during EEH recovery (CR 127062)

During the EEH recovery process while preparing for function reset, the
mbox_sys_shutdown routine  was invoked to shutdown driver's internal mailbox
queue, including the pending (outstanding) mailbox command. There is a window
for a race condition on the pending mailbox command handling when such mailbox
command was just released by the lpfc_sli4_post_async_mbox due to unable to
post such mailbox command because of PCI bus frozen.

commit id: d7069f09884ac3924dacaabbc769cc0b4ee6ad40

Signed-off-by: Maxim Uvarov <maxim.uvarov@oracle.com>