Move SDP templates to its own SDP_Templates.ttcn file

SDP is used in other protocols than MGCP, eg. SIP.

Change-Id: I0610b4cf5533e46a3401c65e60c7cce975c85412
diff --git a/bsc-nat/BSC_MS_ConnectionHandler.ttcn b/bsc-nat/BSC_MS_ConnectionHandler.ttcn
index 1a3f951..8aea74a 100644
--- a/bsc-nat/BSC_MS_ConnectionHandler.ttcn
+++ b/bsc-nat/BSC_MS_ConnectionHandler.ttcn
@@ -24,6 +24,7 @@
 import from MGCP_Types all;
 import from MGCP_Templates all;
 import from SDP_Types all;
+import from SDP_Templates all;
 
 type function void_fn_bsc_ms(charstring id) runs on BSC_MS_ConnHdlr;