s3:net conf: add the same parameter checks to "setparm" as in "net rpc conf".

s3:net conf: add the same parameter checks to "setparm" as in "net rpc conf".

In "net rpc conf" these checks are necessary, since the that command
uses the plain rpc-registry interface at this moment, and so unfortunately
it has to duplicate the checks from the smbconf library.

Since "net conf" uses the registry, these checks are not necessary in
this command. I add them nonetheless to make the output more similar
to "net rpc conf". It is also a little more user friendy than just
printing "INVALID_PARAMETER" as handed back from libsmbconf.

Implement these checks by calling the new net_conf_param_valid() function.

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>