Don't install libnetlink or libnetlink.h
The libnetlink is private to iproute2, and should not be used outside of the project.
libnetlink will not currently link without libutil, which is also private to libnetlink, and not provided by this package.
I could not identify a requirement for libnetlink or its header by any package depending on iproute2, and it should thus be removed to clear confusion from packages such as libmnl or libnl.