move subscr_conn.c to ran_conn.c

subscr_conn.c exclusively defines ran_conn related things. Rename the file.

Change-Id: I6aa6b335842116c717a554c981083a914724ee21
diff --git a/src/libmsc/Makefile.am b/src/libmsc/Makefile.am
index 90bbbf8..9183ff9 100644
--- a/src/libmsc/Makefile.am
+++ b/src/libmsc/Makefile.am
@@ -44,13 +44,13 @@
 	mncc_sock.c \
 	msc_ifaces.c \
 	msc_mgcp.c \
+	ran_conn.c \
 	rrlp.c \
 	silent_call.c \
 	sms_queue.c \
 	transaction.c \
 	osmo_msc.c \
 	ctrl_commands.c \
-	subscr_conn.c \
 	$(NULL)
 if BUILD_IU
 libmsc_a_SOURCES += \