identd: use UNKNOWN for OS name

Some servers like snircd reject OTHER [1], because OTHER can be
used when the ident string is not stable (e.g. is an audit token
that changes each time the ident is queried).

[1]: 17c92003d3/ircd/s_auth.c (L559)

identd/identd.go

@@ -129,7 +129,10 @@ func (s *Identd) handle(c net.Conn) {
 			break
 		}
 
-		fmt.Fprintf(c, "%s : USERID : OTHER : %s\r\n", l, ident)
+		// The "OTHER" operating system may be rejected by IRC servers, because
+		// it may be used when the ident string isn't stable. Use "UNKNOWN"
+		// from RFC 1340 instead.
+		fmt.Fprintf(c, "%s : USERID : UNKNOWN : %s\r\n", l, ident)
 	}
 }