ifconfig: improve vlan options parsing
PR: 261136
Reported by: Daniel O'Connor
Approved by: re(gjb)
MFC after: 2 weeks
(cherry picked from commit 779fd05344662aeec79c29470258bf657318eab3)
(cherry picked from commit 157bf2c9964a54124e05bb7c354d8e5ad784802a)