bnxt_en: Fix randconfig build errors.

Fix undefined symbols when CONFIG_VLAN_8021Q or CONFIG_INET is not set.

Fixes: 8c95f773 ("bnxt_en: add support for Flower based vxlan encap/decap offload")
Reported-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>