smbd: Pass error_context_count through smbd_smb2_request_error_ex()

smbd: Pass error_context_count through smbd_smb2_request_error_ex()

See [MS-SMB2] 2.2.2: This field MUST be set to 0 for SMB dialects
other than 3.1.1. For the SMB dialect 3.1.1, if this field is nonzero,
the ErrorData field MUST be formatted as a variable-length array of
SMB2 ERROR Context structures containing ErrorContextCount entries.

Not used right now yet, but once we start to return STOPPED_ON_SYMLINK properly
this is required.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>