enic: Don't indicate IPv6 pkts using soft-LRO

LRO is only applied to IPv4 pkts, so don't use the LRO indication functions
for anything other IPv4 pkts.  Every non-IPv4 pkt is indicated using non-
LRO functions.

Signed-off-by: Scott Feldman <scofeldm@cisco.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>