mgcp_client: Use INET6_ADDRSTRLEN to store addresses in str format

Warning: This breaks libosmo-mgcp-cli ABI!

Related: SYS#4915
Change-Id: Ib778e9a72764103b52a462ea3c7fb56b23c1bcd6
diff --git a/TODO-RELEASE b/TODO-RELEASE
index e44305b..8c7cd96 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -25,3 +25,4 @@
 #
 #library		what		description / commit summary line
 osmo-mgw        update osmo-gsm-manuals dependency to > 0.3.0 for vty_cpu_sched.adoc include
+libosmo-mgcp-client     mgcp_response, mgcp_conn_peer   struct size change, breaks ABI