team: add support for per-port options

This patch allows to create per-port options. That becomes handy for all
sorts of stuff, for example for userspace driven link-state, 802.3ad
implementation and so on.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>