[NetLabel]: tie NetLabel into the Kconfig system

Modify the net/Kconfig file to enable selecting the NetLabel Kconfig
options.
Signed-off-by: NPaul Moore <paul.moore@hp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/Kconfig

@@ -249,6 +249,8 @@ source "net/ieee80211/Kconfig"
 config WIRELESS_EXT
 	bool
 
+source "net/netlabel/Kconfig"
+
 endif   # if NET
 endmenu # Networking