Alter responder function signature for consistency

Alter responder function signature for consistency

For the responder callback signature, put the closure argument just
after the context, and use KRB5_CALLCONV.  These changes make the
signature consistent with most other libkrb5 callbacks.

(cherry picked from commit 8450ead695639f09862fdcecd46530b1d1b59bfe)

ticket: 7419
version_fixed: 1.11
status: resolved