r26651: libsmb: Allow specifying signing policy from higher up.

r26651: libsmb: Allow specifying signing policy from higher up.

The number of arguments is getting a bit excessive now, so it
probably makes sense to pass in the smbcli_options struct rather than
all members individually and add a convenience function for obtaining a
smbcli_options struct from a loadparm context.
(This used to be commit 9f64213463b5bf3bcbf36913139e9a5042e967a2)