s3: squash 'cast between incompatible function types' warning

s3: squash 'cast between incompatible function types' warning

Some functions (e.g. py_smb_savefile) have an extra unecessary
*kwargs param in their signatures, these definitions are
causing 'cast between incompatible function types' warnings when
compiled with -Wcast-function-type. Some other functions have
the *kwargs which causes "cast between incompatible function types'
warnings which need to be squashed with use of the
PY_DISCARD_FUNC_SIG macro.

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Andreas Schneider <asn@samba.org>