flow_dissector: Check for IP fragmentation even if not using IPv4 address

flow_dissector: Check for IP fragmentation even if not using IPv4 address

This patch corrects the logic for the IPv4 parsing so that it is consistent
with how we handle IPv6.  Specifically if we do not have the flow key
indicating we want the addresses we still may need to take a look at the IP
fragmentation bits and to see if we should stop after we have recognized
the L3 header.

Fixes: 7fdb337cf2e1 ("flow_dissector: Add control/reporting of fragmentation")
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Acked-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>