Do not use the lchan for the paging but operate on the
subscriber_connection, change the signals too to not carry
the lchan but the subscriber connection... the silent call
and vty code still assume there is a lchan inside the
subscriber connection.
With handover and late/early assignment there might be two channels
for one subscriber and only the BSC knows which one to use, so use
the gsm_subscriber_connection everywhere...
This is useful information to know and actually fixes a segfault
in rllp.c where lchan is accessed even tough it could be NULL in
case of failure.
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>