meta-flow: Clean up masking with prerequisities checking.

meta-flow: Clean up masking with prerequisities checking.

Change mf_are_prereqs_ok() take a flow_wildcards pointer, so that the
wildcards can be set at the same time as the prerequisiteis are
checked.  This makes it easier to write more obviously correct code.

Remove the functions mf_mask_field_and_prereqs() and
mf_mask_field_and_prereqs__(), and make the callers first check the
prerequisites, while supplying 'wc' to mf_are_prereqs_ok(), and if
successful, mask the bits of the field that were read or set using
mf_mask_field_masked().

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>