Convert gprs_bssgp_pcu.cpp to C

There's no real use of C++ in that file, and it causes problems when
using llist_head entry macros in future patches adding initial support
for multiple BTS in PCU object, so let's move it to plain C.

Change-Id: Ic771a89fd78b5e66151a5384f0ff6a8895589466
diff --git a/src/decoding.cpp b/src/decoding.cpp
index 0437994..e40496d 100644
--- a/src/decoding.cpp
+++ b/src/decoding.cpp
@@ -291,7 +291,7 @@
 	return num_chunks;
 }
 
-uint8_t Decoding::get_ms_class_by_capability(MS_Radio_Access_capability_t *cap)
+uint8_t get_ms_class_by_capability(MS_Radio_Access_capability_t *cap)
 {
 	int i;
 
@@ -306,7 +306,7 @@
 	return 0;
 }
 
-uint8_t Decoding::get_egprs_ms_class_by_capability(MS_Radio_Access_capability_t *cap)
+uint8_t get_egprs_ms_class_by_capability(MS_Radio_Access_capability_t *cap)
 {
 	int i;