net/sfc: restart TxQ in case of exception on event queue

net/sfc: restart TxQ in case of exception on event queue

Examples of recoverable exceptions because of Tx error are:
 - Tx descriptor PCI read error
 - invalid Tx option descriptor
 - Tx option descriptor not supported by the firmware variant
 - unexpected Tx option descriptor (e.g. missing FATSO2A before
   FATSO2B, missing FATSO2B after FATSO2A)
 - incomplete packet push (CONT bit set in the latest pushed DMA
   descriptor)

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andrew Lee <alee@solarflare.com>
Reviewed-by: Robert Stonehouse <rstonehouse@solarflare.com>