Supply the match mask to prerequisities checking when available.  This
allows checking for zero-valued matches.  Non-zero valued matches
imply the presense of corresponding mask bits, but for zero valued
matches we must explicitly check the mask, too.

This is required now only for conntrack validity checking due to the
conntrack state having and 'invalid' bit, but not 'valid' bit.  One
way to match an valid conntrack state is to match on the 'tracked' bit
being one and 'invalid' bit being zero.  The latter requires the
corresponding mask bit be verified.

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>