ifconfig: add vlanproto "qiniq" as an alias for "802.1ad"

QinQ is better known by this name, so accept it as an alias

Reported-by: Mike Geiger
Reviewed-by: melifaro, hselasky, rpokala
MFC-with: 366917
Sponsored-by: Klara Inc.
Differential-Revision: https://reviews.freebsd.org/D28245