repair gdbstub to match the gdbserial protocol specification

The gdbserial protocol handler should return an empty packet instead
of an error string when ever it responds to a command it does not
implement.

The problem cases come from a debugger client sending
qTBuffer, qTStatus, qSearch, qSupported.

The incorrect response from the gdbstub leads the debugger clients to
not function correctly.  Recent versions of gdb will not detach correctly as a result of this behavior.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>

kernel/debug/gdbstub.c

@@ -621,10 +621,8 @@ static void gdb_cmd_query(struct kgdb_state *ks)
 	switch (remcom_in_buffer[1]) {
 	case 's':
 	case 'f':
-		if (memcmp(remcom_in_buffer + 2, "ThreadInfo", 10)) {
-			error_packet(remcom_out_buffer, -EINVAL);
+		if (memcmp(remcom_in_buffer + 2, "ThreadInfo", 10))
 			break;
-		}
 
 		i = 0;
 		remcom_out_buffer[0] = 'm';
@@ -665,10 +663,9 @@ static void gdb_cmd_query(struct kgdb_state *ks)
 		pack_threadid(remcom_out_buffer + 2, thref);
 		break;
 	case 'T':
-		if (memcmp(remcom_in_buffer + 1, "ThreadExtraInfo,", 16)) {
-			error_packet(remcom_out_buffer, -EINVAL);
+		if (memcmp(remcom_in_buffer + 1, "ThreadExtraInfo,", 16))
 			break;
-		}
+
 		ks->threadid = 0;
 		ptr = remcom_in_buffer + 17;
 		kgdb_hex2long(&ptr, &ks->threadid);