Merge bts_alloc_ms() and ms_alloc()

gprs_default_cb_ms_idle() is changed to have the same implementation as
previous bts_ms_idle_cb(), since that's the only one being used in
osmo-pcu code. It makes no sense to use different callback logic in unit
tests.

This is another step towards simplifying the code and getting rid of the
idle/active_cb().

Change-Id: I2a06d17588572a21dc5a14ddbde83766076b446d
diff --git a/src/pdch.cpp b/src/pdch.cpp
index 43b3936..1c39ceb 100644
--- a/src/pdch.cpp
+++ b/src/pdch.cpp
@@ -665,7 +665,7 @@
 		uint32_t tlli = request->ID.u.TLLI;
 		ms = bts_get_ms_by_tlli(bts, tlli, GSM_RESERVED_TMSI);
 		if (!ms) {
-			ms = bts_alloc_ms(bts);
+			ms = ms_alloc(bts);
 			ms_set_tlli(ms, tlli);
 		}
 	} else if (request->ID.u.Global_TFI.UnionType) { /* ID_TYPE = DL_TFI */
@@ -857,7 +857,7 @@
 	if (!ms) {
 		LOGPDCH(this, DRLCMAC, LOGL_NOTICE, "MS send measurement "
 			"but TLLI 0x%08x is unknown\n", report->TLLI);
-		ms = bts_alloc_ms(bts());
+		ms = ms_alloc(bts());
 		ms_set_tlli(ms, report->TLLI);
 	}
 	if ((poll = pdch_ulc_get_node(ulc, fn))) {