pipeline: relax table match field requirements

pipeline: relax table match field requirements

The match fields for a given table have to be part of the same header
or the metadata structure. This commit removes the requirement that
the list of match fields must observe the order of fields within their
structure. For example, the h.ipv4.dst_addr field can now be listed
before the h.ipv4.src_addr field in a table match field list, even
though within the IPv4 header the dst_addr field is present after the
src_addr field.

Signed-off-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>