lib:param: Set a memory context for the globals if not initialized yet

lib:param: Set a memory context for the globals if not initialized yet

Typically once the smb.conf starts to be loaded,
loadparm_s3_init_globals() will be called and a memory context for
strings on the static Globals will be created.  But we might call
lpcfg_set_cmdline() before we load the smb.conf file, so we (via a
helper pointer) call loadparm_s3_init_globals() to get that
initialisation done earlier, ensuring that all allocations on Globals is
done on a memory context that we can later TALLOC_FREE() before exit().

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>