Take the ifnet's address lock in igmp_v3_cancel_link_timers().

inm_rele_locked() may remove the multicast address associated with inm.

Reported by: syzbot+871c5d1fd5fac6c28f52@syzkaller.appspotmail.com
Reviewed by: hselasky
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D23009