Add an ability to punt all unknown UDP traffic to the host

By default, VPP replies with ICMP error: port unreachable when receives
an ‘unknown’ UDP (destination port with no registered listener) packet.

An existing punt() API is extended to accept ALL (~0) as a L4 port
number and if used redirects all ‘unknown’ UDP packets to the host.

New ‘all’ option is added to the “set punt udp” CLI as well.

Change-Id: I444fc5e32ffa3f0f085bb17708bf32b883ba09df
Signed-off-by: Alexander Popovsky (apopovsk) <apopovsk@cisco.com>