mgcp_sdp: mgcp_sdp.c does not include own header file

The header file mgcp_sdp.h is not included by mgcp_sdp.c. Lets include
it here as well in order to be complete.

Change-Id: I3d9f28d6e7ca027b1be25d775a6a75d0fc491a50
diff --git a/src/libosmo-mgcp/mgcp_sdp.c b/src/libosmo-mgcp/mgcp_sdp.c
index 85b8801..c84f32c 100644
--- a/src/libosmo-mgcp/mgcp_sdp.c
+++ b/src/libosmo-mgcp/mgcp_sdp.c
@@ -26,6 +26,7 @@
 #include <osmocom/mgcp/mgcp_msg.h>
 #include <osmocom/mgcp/mgcp_endp.h>
 #include <osmocom/mgcp/mgcp_codec.h>
+#include <osmocom/mgcp/mgcp_sdp.h>
 
 #include <errno.h>