ksmbd: preserve compound responses for chained errors

ksmbd: preserve compound responses for chained errors

set_smb2_rsp_status() resets the response iov and compound offsets before
building an error response. That is fine for a single request, but it
corrupts a compound response when an error is detected after an earlier
compound element has already been completed.

smb2.compound.invalid4 sends a READ as the first compound element and a
bogus command as the second one. The READ response must remain in
the compound response with STATUS_END_OF_FILE, followed by the bogus
command response with STATUS_INVALID_PARAMETER. Resetting the response
state for the second command breaks the compound framing and the client
reports NT_STATUS_INVALID_NETWORK_RESPONSE.

When setting an error for a chained command, update and pin only
the current compound response slot instead of resetting the whole response.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>