optimize: merge verdict maps with same lookup key

optimize: merge verdict maps with same lookup key

Merge two consecutive verdict maps with the same lookup key.

For instance, merge the following:

 table inet x {
        chain filter_in_tcp {
                tcp dport vmap {
                           80 : accept,
                           81 : accept,
                          443 : accept,
                          931 : accept,
                         5001 : accept,
                         5201 : accept,
                }
                tcp dport vmap {
                         6800-6999  : accept,
                        33434-33499 : accept,
                }
        }
 }

into:

 table inet x {
        chain filter_in_tcp {
                tcp dport vmap {
                           80 : accept,
                           81 : accept,
                          443 : accept,
                          931 : accept,
                         5001 : accept,
                         5201 : accept,
                         6800-6999  : accept,
                        33434-33499 : accept,
                }
	}
 }

This patch updates statement comparison routine to inspect the verdict
expression type to detect possible merger.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>