MAINTAINERS: exclude wireless drivers from netdev

It seems that we mostly get netdev CCed on wireless patches
which are written by people who don't know any better and
CC everything that get_maintainers spits out. Rather than
patches which indeed could benefit from general networking
review.

Marking them down in patchwork as Awaiting Upstream is
a bit tedious.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Kalle Valo <kvalo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>