Handle XID frames in src/server.c

Handle XID frames in src/server.c by decoding the parameter information
and passing it to patty_ax25_sock_params_set()

src/server.c

@@ -1321,12 +1321,20 @@ static int handle_xid(patty_ax25_server *server,
     }
 
     /*
-     * TODO: Actually do something with the parameters received; also perhaps
-     * consider replying to this XID frame with another XID frame
+     * Since we've received an XID packet, we can assume that the remote
+     * station is capable of speaking AX.25 v2.2.  Therefore, we should
+     * upgrade the socket defaults accordingly, and negotiate downwards
+     * as necessary.
      */
+    patty_ax25_sock_upgrade(sock);
+
+    if (patty_ax25_sock_params_set(sock, &params) < 0) {
+        goto error_sock_params_set;
+    }
 
     return 0;
 
+error_sock_params_set:
 error_io:
     return -1;
 }