Pass paging group instead of imsi where later is not needed

Change-Id: Id0663a81f439f2d0b893b0d34f85a6db1927ef8e
diff --git a/src/bts.cpp b/src/bts.cpp
index 71a2f06..5e1725c 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -890,7 +890,7 @@
 	return 0;
 }
 
-void BTS::snd_dl_ass(gprs_rlcmac_tbf *tbf, bool poll, const char *imsi)
+void BTS::snd_dl_ass(gprs_rlcmac_tbf *tbf, bool poll, uint16_t pgroup)
 {
 	int plen;
 	unsigned int ts = tbf->first_ts;
@@ -910,7 +910,7 @@
 						    GSM_L1_BURST_TYPE_ACCESS_0);
 	if (plen >= 0) {
 		immediate_assignment_dl_tbf();
-		pcu_l1if_tx_pch(immediate_assignment, plen, imsi);
+		pcu_l1if_tx_pch(immediate_assignment, plen, pgroup);
 	}
 
 	bitvec_free(immediate_assignment);