netinet: Add IPPROTO_IGMP definition

Add the definition of Internet Group Management Protocol.

Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Thomas Graf <tgraf@redhat.com>
Signed-off-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
packets: Add igmp header definitions

Add basic header structure and definitions into packet.h.

Acked-by: Thomas Graf <tgraf@redhat.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>