gprs_rlcmac: convert from C++ to C

Change-Id: I7260ad1a67ebdc09767a679e579fead262f1627a
diff --git a/src/encoding.cpp b/src/encoding.cpp
index 243c874..6b626cc 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -801,7 +801,7 @@
 }
 
 /* Generate paging request. See 44.018, sections 10 and 9.1.22 */
-int Encoding::write_paging_request(bitvec * dest, const struct osmo_mobile_identity *mi)
+int write_paging_request(struct bitvec *dest, const struct osmo_mobile_identity *mi)
 {
 	uint8_t mi_buf[GSM48_MID_MAX_SIZE];
 	int mi_len;