iptables: fix build with older kernel headers

iptables: fix build with older kernel headers

iptables version 1.6.2 uses the BPF_OBJ_GET macro that is only available
since kernel version 4.4. Add a patch fixing the detection of the
feature availability.

Fixes:
http://autobuild.buildroot.net/results/e67/e670548c4b250e8a102a4929cafa85634fc79a3d/
http://autobuild.buildroot.net/results/1a7/1a7ab509440c9acacf606f238b8989d9b4287d52/
http://autobuild.buildroot.net/results/555/55583e20bcdf602132c074e08d1a49507d5a48ad/

Cc: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>