fix vlan locking to permit sx acquisition in ioctl calls

• update vlan(9) to handle changes earlier this year in multicast locking

Tested by: np@, darkfiberu at gmail.com

PR: 230510
Reviewed by: mjoras@, shurd@, sbruno@
Approved by: re (gjb@)
Sponsored by: Limelight Networks
Differential Revision: https://reviews.freebsd.org/D16808