Windows: Make use of SMB interface a runtime decision

Windows: Make use of SMB interface a runtime decision

Add 'smb_Enabled' and 'RDR_Initialized' flag variables.
Default smb_Enabled to true and RDR_Initialized to false.

Add registry value "SMBInterfaceEnabled" to permit disabling
the SMB interface.

If the redirector interface is initialized (a future set of
patchsets will add it) disable the SMB interface at runtime.

Change-Id: I354e121001d942421aa98490b62b710ac175051f
Reviewed-on: http://gerrit.openafs.org/5337
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>