mncc: Update the protocol to match LCR

This adds the protocol definition for the RTP bridge extension
of Andreas Eversberg and bumps the protocol version.

I added the missing mncc mappings from value to string.

[ 5cf8fb10ea3addcae74d37f4dbf1c1be664df53e protocol extension
  5dac90de38990b188f499c602bf18a4f232070e8 payload extension]
diff --git a/openbsc/src/libmsc/mncc.c b/openbsc/src/libmsc/mncc.c
index 73db5f0..2767faa 100644
--- a/openbsc/src/libmsc/mncc.c
+++ b/openbsc/src/libmsc/mncc.c
@@ -83,6 +83,9 @@
 	{"MNCC_FRAME_RECV",	0x0201},
 	{"MNCC_FRAME_DROP",	0x0202},
 	{"MNCC_LCHAN_MODIFY",	0x0203},
+	{"MNCC_RTP_CREATE",	0x0204},
+	{"MNCC_RTP_CONNECT",	0x0205},
+	{"MNCC_RTP_FREE",	0x0206},
 
 	{"GSM_TCHF_FRAME",	0x0300},
 	{"GSM_TCHF_FRAME_EFR",	0x0301},