packets: use flow protocol when recalculating ipv6 checksums

packets: use flow protocol when recalculating ipv6 checksums

When using masked actions the ipv6_proto field of an action
to set IPv6 fields may be zero rather than the prevailing protocol
which will result in skipping checksum recalculation.

This patch resolves the problem by relying on the protocol
in the packet rather than that in the set field action.

A similar fix for the kernel datapath has been accepted into David Miller's
'net' tree as b4f70527f052 ("openvswitch: use flow protocol when
recalculating ipv6 checksums").

Cc: Jarno Rajahalme <jrajahalme@nicira.com>
Fixes: 6d670e7f0d45 ("lib/odp: Masked set action execution and printing.")
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Acked-by: Ben Pfaff <blp@ovn.org>