mesh: Use setup completion callback to complete mesh join

mesh: Use setup completion callback to complete mesh join

Mesh join function is the last function to be called during mesh join
process, but it's been called a bit earlier than it's supposed to be, so
that some mesh parameter values such as VHT capabilities were not
applied correct when mesh join is in process. Moreover, the current
design of mesh join that is called directly after mesh initialization
isn't suitable for DFS channels to use, since mesh join process should
be paused until DFS CAC is done and resumed after it's done.

The callback will be called by hostapd_setup_interface_complete_sync().
There is a possibility that completing mesh init fails, so add error
handling codes for that.

Signed-off-by: Peter Oh <peter.oh@bowerswilkins.com>