Changes

cosmetic: eliminate else-after-return in gsmtap_csd_rlp_process()

The code in this function used else-after-return constructs, which
are now rejected by the linter for newly committed code.  This
function needs to be moved to a new source file, which will cause
it to be treated as new code by the linter - hence fix this code
style issue first.

Change-Id: Ide00e819222bb0173eca42ee3714db7f7e1a6d1e