Pass paging group instead of imsi where later is not needed

Change-Id: Id0663a81f439f2d0b893b0d34f85a6db1927ef8e
diff --git a/src/bts.h b/src/bts.h
index 0eaab85..823138b 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -306,7 +306,7 @@
 		enum ph_burst_type burst_type);
 	int rcv_ptcch_rach(uint8_t trx_nr, uint8_t ts_nr, uint32_t fn, int16_t qta);
 
-	void snd_dl_ass(gprs_rlcmac_tbf *tbf, bool poll, const char *imsi);
+	void snd_dl_ass(gprs_rlcmac_tbf *tbf, bool poll, uint16_t pgroup);
 
 	GprsMsStorage &ms_store();
 	GprsMs *ms_by_tlli(uint32_t tlli, uint32_t old_tlli = 0);