mac80211: support userspace MPM

Earlier mac80211 would check whether some kind of mesh
security was enabled, when the real question was "is the
MPM in userspace"?

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
nl80211: user_mpm overrides auto_open_plinks

If the user requested a userspace MPM, automatically
disable auto_open_plinks to fully disable the kernel MPM.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
mac80211: disallow changing auto_open_plinks

while user MPM is running.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
mac80211: init mesh timer for user authed STAs

There is a corner case which wasn't being covered:
userspace may authenticate and allocate stations,
but still leave the peering up to the kernel.

Initialize the peering timer if the MPM is in userspace in
a path which is taken when allocating stations from both
the kernel and userspace.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>