socket: Introduce function to obtain socket name

Using this function, one can obtain a human-readable string identifying
the host and port names of the socket.

Change-Id: Ib5de5c7b9effe1b0a363e4473a7be7fa38ca6ef3
diff --git a/TODO-RELEASE b/TODO-RELEASE
index fb0bfea..5c6bfa3 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -7,3 +7,4 @@
 # If any interfaces have been added since the last public release: c:r:a + 1.
 # If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what			description / commit summary line
+libosmocore	new function		osmo_sock_get_name()