s3-netapi Add libnetapi_net_init(), don't double-init common Samba subsystems

s3-netapi Add libnetapi_net_init(), don't double-init common Samba subsystems

The issue here is that libnet and net were both trying to load the
smb.conf files, the case tables and set the debug levels.  The set of
the debug levels caused problems, because it would force the level to
0, not (say) 10 as requested on the command line.

This regression was apparently introduced in
cf4de8ec2c8df2ceabbe3d836d296b058e7b19fb when eliminating
AllowDebugChange.

Andrew Bartlett