hostapd: fix goto loop for ubus assoc handler

hostapd: fix goto loop for ubus assoc handler

When a ubus event handler denies a association with a non-zero return
value, the code jumps to preceeding code, creating an endless loop until
the event handler accepts the assc request.

Move the ubus handler further up the code to avoid creating such a loop.

Signed-off-by: David Bauer <mail@david-bauer.net>