sgsn: Do not 'commit' implicitely when executing 'insert'

Currently the gprs_subscr_update function is called when the
'update-subscriber ... insert ...' command is executed. This will
eventually notify the GMM layer which is rather the purpose of the
'commit' command.

This patch removes the call from update_subscr_insert.

Sponsored-by: On-Waves ehf
sgsn: Integrate Auth & Ciph into gsm48_gmm_authorize

Currently the Authentication and Ciphering procedure is not yet
invoked by the GMM layer.

This patch starts this procedure from within gsm48_gmm_authorize when
the mm->auth_state has been set to SGSN_AUTH_AUTHENTICATE and a call
to gsm0408_gprs_authenticate has been issued directly or indirectly
by the call to sgsn_auth_request.

Sponsored-by: On-Waves ehf
sgsn: Support subscriber based authentication

This commit mainly extends sgsn_auth.c to use and support the
auth_state SGSN_AUTH_AUTHENTICATE. It will be activated when IMSI and
IMEI are available, authentication is required
(subscr->sgsn_data->authenticate is set), but the MM context is not
marked as authenticated. If the state has been set to
SGSN_AUTH_AUTHENTICATE and sgsn_auth_update() is called, the GMM
layer will be informed by invoking gsm0408_gprs_authenticate().

Sponsored-by: On-Waves ehf