skeleton: fix indentation of generated interfaces file

The generated $(TARGET_DIR)/etc/network/interfaces mixes spaces and
tabs. Fix by using tabs only.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/skeleton/skeleton.mk

@@ -148,7 +148,7 @@ define SET_NETWORK_DHCP
 		echo ;                                               \
 		echo "auto $(NETWORK_DHCP_IFACE)";                   \
 		echo "iface $(NETWORK_DHCP_IFACE) inet dhcp";        \
-		echo "  pre-up /etc/network/nfs_check";              \
+		echo "	pre-up /etc/network/nfs_check";              \
 		echo "	wait-delay 15";                              \
 	) >> $(TARGET_DIR)/etc/network/interfaces
 	$(INSTALL) -m 0755 -D $(SKELETON_PKGDIR)/nfs_check \