package/dhcp: Fix config name

ISC dhcp is no longer the only way of handling DHCP, so use a less generic
config text.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/dhcp/Config.in

@@ -1,5 +1,5 @@
 config BR2_PACKAGE_DHCP
-	bool "DHCP support"
+	bool "isc dhcp"
 	help
 	  DHCP relay agent from the ISC DHCP distribution.