spectrum: Add a delayed work to update SPAN buffsize according to speed

When PUDE event is handled and the link is up, update the port SPAN
buffer size according to the current speed.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>