buildroot

network-manager: needs kernel headers v3.7

NetworkManager uses struct ifla_vxlan_port_range that was introduced in kernel
version 3.7.

Fixes:
http://autobuild.buildroot.net/results/6f2/6f214e3206ad0b12c633a7632c1e32c369e447ff/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>