Add IGMPv3 support.

Add IGMPv3 support.

Support IGMPv3 messages with multiple records. Make sure all IGMPv3
messages go through slow path, since they may carry multiple multicast
addresses, unlike IGMPv2.

Tests done:

* multiple addresses in IGMPv3 report are inserted in mdb;
* address is removed from IGMPv3 if record is INCLUDE_MODE;
* reports sent on a burst with same flow all go to userspace;
* IGMPv3 reports go to mrouters, i.e., ports that have issued a query.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ben Pfaff <blp@nicira.com>