Changes

cosmetic: move gsmtap_csd_rlp_process() to csd_rlp.c

The next patch in the series will add code for alignment of downlink
RLP frames in CSD NT modes; that code will go into new file csd_rlp.c.
RLP GSMTAP code logically belongs in the same place - hence move it
there in preparation.

Change-Id: I824ce6614c8591cccc5f6bcdde767fe49d551378