openvswitch: retain parsed IPv6 header fields in flow on error skipping extension headers

When an error occurs skipping IPv6 extension headers retain the already
parsed IP protocol and IPv6 addresses in the flow. Also assume that the
packet is not a fragment in the absence of information to the contrary;
that is always use the frag_off value set by ipv6_skip_exthdr().

This allows matching on the IP protocol and IPv6 addresses of packets
with malformed extension headers.

Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>