build: remove non-portable rule

> Makefile.am:97: `%'-style pattern rules are a GNU make extension

(iptables still requires GNU make for extensions/, because it is
so much easier to write.)

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
1 file changed