cfg80211/nl80211: Add userspace authentication flag to mesh setup

During mesh setup, use NL80211_MESH_SETUP_USERSPACE_AUTH flag to create
a secure mesh and route management frames to userspace.

Also, NL80211_CMD_GET_WIPHY now returns a flag NL80211_SUPPORT_MESH_AUTH
if the wiphy's mesh implementation supports routing of mesh auth frames
to userspace.  This is useful for forward compatibility between old
kernels and new userspace tools.

Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>