wlanstat(8): Rename from wlanstats(8) to keep consistency

All the status and statistics utilties in base are ending with "stat",
the only exception is mailstats(8) but that's from sendmail.

Reviewed by: imp, adrian
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52724

(cherry picked from commit 89eee8ee2ce57b7884defb8f9af016cd28ef1562)