wpa-supplicant: Get 802.11s ssid information from option mesh_id

wpa-supplicant: Get 802.11s ssid information from option mesh_id

The scripts for authsae and iw use the option mesh_id to get set the
"meshid" during a mesh join. But the script for wpad-mesh ignores the
option mesh_id and instead uses the option ssid. Unify the mesh
configuration and let the wpa_supplicant script also use the mesh_id from
the configuration.

Signed-off-by: Sven Eckelmann <sven@open-mesh.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47615 3c298f89-4303-0410-b956-a3cf2f4a3e73