network.subr: adjust regex for wlans_xxxxx rc.conf entries

Drivers like ath1[012]k will not match the current wlans_*-regex as
they have digits followed by letters. Adjust the regex to allow
this combination in order to be able to configure interfaces with
names like wlans_ath11k0="..."

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D39674

(cherry picked from commit de1dde5dfea4407119955a6f94528396b258db3f)