sdp: allow more space for fmtp

In osmo-mgw, we recently chose 256 for maximum fmtp length.
Adjust to that here, too.

Change-Id: Ib9b9608d8d8f7ce34596a950dbc480e8a72ebf97
diff --git a/include/osmocom/msc/sdp_msg.h b/include/osmocom/msc/sdp_msg.h
index e62f22b..724440c 100644
--- a/include/osmocom/msc/sdp_msg.h
+++ b/include/osmocom/msc/sdp_msg.h
@@ -25,7 +25,7 @@
 	/* Like "GSM", "AMR", "EFR", ... */
 	char subtype_name[16];
 	unsigned int rate;
-	char fmtp[64];
+	char fmtp[256];
 };
 
 struct sdp_audio_codecs {