edge: Select implementation by mode in rlc_data_to_dl_append

Currently the GPRS data block encoding is applied to every
coding scheme, even if an MCS is selected.

This commit renames the actual encoding function to
rlc_data_to_dl_append_gprs (not exported) and puts
selection code into Encoding::rlc_data_to_dl_append. This
requires an additional cs argument.

Sponsored-by: On-Waves ehf
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index 35c3ccb..5607e9e 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -484,7 +484,7 @@
 
 		is_final = llc_queue()->size() == 0 && !keep_open(fn);
 
-		ar = Encoding::rlc_data_to_dl_append(rdbi,
+		ar = Encoding::rlc_data_to_dl_append(rdbi, cs,
 			&m_llc, &write_offset, &num_chunks, data, is_final);
 
 		if (ar == Encoding::AR_NEED_MORE_BLOCKS)