veth: grab a reference for rtnl_link_veth_get_peer()

So that users could keep a refcount for the peer.
The capability trick is from Thomas Haller.

Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Thomas Haller <thaller@redhat.com>
act: grab a reference when adding an action to a filter

When we add an action to a filter, its lifetime becomes
same with the filter. So in case user frees it before
us, we could just grab a reference here.

Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>