MCS: move HeaderType enum outside of class definition

Move functions which compute number of blocks or bits depending on
header type and corresponding enum outside of GprsCodingScheme
class. This will allows us to use standard libosmocore value_sting
functions in upcoming patches for IA Rest Octet encoding/decoding.

Change-Id: Id0873f85e1f16a72e17e7fbc4ad76b194917067f
diff --git a/src/decoding.cpp b/src/decoding.cpp
index 0dbb10a..3410291 100644
--- a/src/decoding.cpp
+++ b/src/decoding.cpp
@@ -355,16 +355,16 @@
 {
 	unsigned int cur_bit = 0;
 	switch(cs.headerTypeData()) {
-	case GprsCodingScheme::HEADER_GPRS_DATA :
+	case HEADER_GPRS_DATA :
 		cur_bit = rlc_parse_ul_data_header_gprs(rlc, data, cs);
 		break;
-	case GprsCodingScheme::HEADER_EGPRS_DATA_TYPE_3 :
+	case HEADER_EGPRS_DATA_TYPE_3 :
 		cur_bit = rlc_parse_ul_data_header_egprs_type_3(rlc, data, cs);
 		break;
-	case GprsCodingScheme::HEADER_EGPRS_DATA_TYPE_2 :
+	case HEADER_EGPRS_DATA_TYPE_2 :
 		cur_bit = rlc_parse_ul_data_header_egprs_type_2(rlc, data, cs);
 		break;
-	case GprsCodingScheme::HEADER_EGPRS_DATA_TYPE_1 :
+	case HEADER_EGPRS_DATA_TYPE_1 :
 		cur_bit = rlc_parse_ul_data_header_egprs_type_1(rlc, data, cs);
 		break;
 	default: