bgpd: bgp pbr ignores bgp fs entries with 0.0.0.0 ips written.

bgpd: bgp pbr ignores bgp fs entries with 0.0.0.0 ips written.

when converting bgp fs entries to bgp pbr entries, the fields of the
flowspec are analysed. In the case src ip or dst ip is set to 0.0.0.0,
that field is ignored, thus preventing from injecting a rule that can
not be injected into the pbr. This can be done by avoiding mentioning
the field in the bitmask structure used to convert data to pbr entries.

PR=61620
Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
Acked-by: Emmanuel Vize <emmanuel.vize@6wind.com>