iproute2: Allow compiling against libbpf

This adds a configure check for libbpf and renames functions to allow
lib/bpf.c to be compiled with it present. This makes it possible to
port functionality piecemeal to use libbpf.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
4 files changed