target/rd: Allow WriteCacheEnabled=1 operation with rd_mcp backends

This patch adds the missing rd_mcp_template->write_cache_emulated=1 bit to
optionally allow WriteCacheEnabled=1 (WCE) to be enabled for the built-in
TCM/rd_mcp backend driver.

Tested on v3.6-rc[0,2] code with loopback+tcm_vhost fabric ports.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_rd.c

@@ -474,6 +474,7 @@ static int rd_parse_cdb(struct se_cmd *cmd)
 static struct se_subsystem_api rd_mcp_template = {
 	.name			= "rd_mcp",
 	.transport_type		= TRANSPORT_PLUGIN_VHBA_VDEV,
+	.write_cache_emulated	= 1,
 	.attach_hba		= rd_attach_hba,
 	.detach_hba		= rd_detach_hba,
 	.allocate_virtdevice	= rd_allocate_virtdevice,