Since r344530 we've switch libifconfig as an internallib so it's not installed.
Do not install the header too.
This "solves" a problem with pkgbase where a libifconfig-development package
is created and due to how packages are created we add a dependency to a
libifconfig package that doesn't exists.
Reported by: pizzamig
Signed-off-by: Emmanuel Vadot <email@example.com>