link: Fix af_ops leak on ENOMEM

Signed-off-by: Thomas Graf <tgraf@suug.ch>
link: Keep reference to af_ops during lifetime of link object

Signed-off-by: Thomas Graf <tgraf@suug.ch>
link: Modify link policy on the stack

Signed-off-by: Thomas Graf <tgraf@suug.ch>
link: Hold af_ops reference for each AF_SPEC block during lifetime of link object

Signed-off-by: Thomas Graf <tgraf@suug.ch>
link: Free and realloc af specific data upon rtnl_link_set_family()

Signed-off-by: Thomas Graf <tgraf@suug.ch>