For GPRS the look-up via bts/trx does not make any sense and would
introduce bad depdencies for the SGSN. Move the look-up code to a
new file and introduce new setup methods.
Coverity complains about the saveptr used in the strtok_r. This
is not a bug because we pass a string as part of the first call
to strtok_r but it is easier to just initialize it.
Addresses: Coverity CID 1042323
Move to the control command handling out of the main file into
a dedicated module. There are still some calls embedded into the
main code but it will be moved soon.