fm10k: don't handle mailbox events in iov_event path and always process mailbox

Since we already schedule the service task, we can just wait for this
task to handle the mailbox events from the VF. This reduces some complex
code flow, and makes it so we have a single path for handling the VF
messages. There is a possibility that we have a slight delay in handling
VF messages, but it should be minimal.

The result of tx_complete and !rx_ready is insufficient to determine
whether we need to process the mailbox. There is a possible race
condition whereby the VF fills up the mbmem for us, but we have already
recently processed the mailboxes in the interrupt. During this time,
the interrupt is disabled. Thus, our Rx FIFO is empty, but the mbmem now
has data in it. Since we continually check whether Rx FIFO is empty, we
then never call process. This results in the possibility to prevent PF
from handling the VF mailbox messages.

Instead, just call process every time, despite the fact that we may or
may not have anything to process for the VF. There should be minimal
overhead for doing this, and it resolves an issue where the VF never
comes up due to never getting response for its SET_LPORT_STATE message.

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