fm10k: ensure we process SM mbx when processing VF mbx

When we process VF mailboxes, the driver is likely going to also queue
up messages to the switch manager. This process merely queues up the
FIFO, but doesn't actually begin the transmission process. Because we
hold the mailbox lock during this VF processing, the PF<->SM mailbox is
not getting processed at this time. Ensure that we actually process the
PF<->SM mailbox in between each PF<->VF mailbox.

This should ensure prompt transmission of the messages queued up after
each VF message is received and handled.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>