When we support multiple vlans, we must issue announce to all
supported vlans. Same applies to sync/follow-up. This changes
state-master.c to do the sending several times.

Initially I changed msg.c (for the announce message only), this saved
the repeated call to msg_pack_announce() but by doing it at
state-master level I have simpler code and layer consistency (doing
sync/fup at msg.c level would be a mess).
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>