wlanstats: add -Wno-cast-align back for now

After fixing the obvious build and cast error when moving this from tools
to usr.sbin and removing -Wno-cast-align, re-add it back as at least
powerpc* does not compile without it (amd64, arm64, and i386 were ok).

In general wlanstats may now get a bit more love after 22 years of
being in the tree and being moved at least twice.
But first unbreak things again.

Reported by: mmel, cperciva (weekly snapshots)
Sponsored by: The FreeBSD Foundation
Fixes: 61ce422531805
MFC after: 3 days