ionic: account for vlan tag len in rx buffer len

Let the FW know we have enough receive buffer space for the
vlan tag if it isn't stripped.

Fixes: 0f3154e6 ("ionic: Add Tx and Rx handling")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Link: https://lore.kernel.org/r/20201218215001.64696-1-snelson@pensando.io


Signed-off-by: Jakub Kicinski <kuba@kernel.org>