lib/odp: Fix handling of set masked action in parse_odp_action

lib/odp: Fix handling of set masked action in parse_odp_action

If we find that we need to change from a SET to SET_MASKED action,
then we write the mask to the actions opfbuf. But if there was netlink
pad added to the buffer when writing the key, mask won't follow the
key data as per SET_MASKED spec.

Fix that by removing the padding before writing the mask, and
readding it if needed for alignment.

Fixes: 6d670e7f0d45 ("lib/odp: Masked set action execution and printing.")
Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>