client/common: move constant MGCP_ENDPOINT_MAXLEN

MGCP_ENDPOINT_MAXLEN is currently only defined for the mgcp client,
since this is in general a common parameter it should be moved to
mgcp_common.h so that both sides can use it.

Change-Id: I9e1c52aa5ebd83b2d9e5178ea24cb27d96cb7ddd
diff --git a/include/osmocom/mgcp/mgcp_common.h b/include/osmocom/mgcp/mgcp_common.h
index 29dc458..7684936 100644
--- a/include/osmocom/mgcp/mgcp_common.h
+++ b/include/osmocom/mgcp/mgcp_common.h
@@ -72,4 +72,8 @@
  * (see also RFC3435 2.1.3.2 Names of Connections) */
 #define MGCP_CONN_ID_LENGTH 32+1
 
+/* String length of Endpoint Identifiers.
+/  (see also RFC3435 section 3.2.1.3) */
+#define MGCP_ENDPOINT_MAXLEN (255*2+1+1)
+
 #endif