Change the way as_compare() and aspath_match() handle 'neighbor-as'. Instead

Change the way as_compare() and aspath_match() handle 'neighbor-as'. Instead
of doing the condition before calling aspath_match() just pass the neighbor-as
down to as_compare() which then has all needed data for the lookup. While
doing this also remove one of the as fields in struct filter_as since the
min/max fields can be reused for unary operations.
OK denis@ phessler@