extensions: libxt_bpf: support ebpf pinned objects

extensions: libxt_bpf: support ebpf pinned objects

Exercise the new kernel feature introduced in commit 2c16d6033264
("netfilter: xt_bpf: support ebpf") to load pinned eBPF programs.

The new interface allows instantiating a bpf match using

  -m bpf --object-pinned ${PATH}

where ${PATH} points to a node in a bpf virtual filesystem. See
also the revised man page.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>