xps: Add CONFIG_XPS

This patch adds XPS_CONFIG option to enable and disable XPS.  This is
done in the same manner as RPS_CONFIG.  This is also fixes build
failure in XPS code when SMP is not enabled.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/Kconfig b/net/Kconfig
index 55fd82e9..126c2af 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -220,6 +220,11 @@
 	depends on SMP && SYSFS && USE_GENERIC_SMP_HELPERS
 	default y
 
+config XPS
+	boolean
+	depends on SMP && SYSFS && USE_GENERIC_SMP_HELPERS
+	default y
+
 menu "Network testing"
 
 config NET_PKTGEN