gprs_sndcp_comp_free: Replace ifelse with switch and better handling of error

gprs_sndcp_dcomp_term asserts if compclass is not
SNDCP_XID_DATA_COMPRESSION, so this way by checking in the caller too we
easily now if the unexpected value is in compclass or in algo.dcomp.

Change-Id: I4600e6a137f42f20fdf69637e4a9048b265c1748
1 file changed