when paging is successfull, the paging_request_stop() function is called
with the current lchan, so the callback function will be called. for all
other bts', the paging_request_stop() function is called without lchan,
so the paging is stopped, but the callback function is not called.
this ensures that only one paging result is received when paging
multiple BTS. (Andreas Eversberg)
Harald Welte