openvswitch: take into account de-fragmentation/gso_size in execute_check_pkt_len

ovs connection tracking module performs de-fragmentation on incoming
fragmented traffic. Take info account if traffic has been de-fragmented
in execute_check_pkt_len action otherwise we will perform the wrong
nested action considering the original packet size. This issue typically
occurs if ovs-vswitchd adds a rule in the pipeline that requires connection
tracking (e.g. OVN stateful ACLs) before execute_check_pkt_len action.
Moreover take into account GSO fragment size for GSO packet in
execute_check_pkt_len routine

Fixes: 4d5ec89f

 ("net: openvswitch: Add a new action check_pkt_len")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>