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>