nfp: correct RX buffer length calculation

When calculating the RX buffer length we need to account
for up to 2 VLAN tags.  Rounding up to 1k is an relic of
a distant past and can be removed.  While at it also remove
trivial print statement.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>