openvswitch: Handle NF_REPEAT in conntrack action.

Repeat the nf_conntrack_in() call when it returns NF_REPEAT.  This
avoids dropping a SYN packet re-opening an existing TCP connection.

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>