net: dsa: Pass pcs_poll flag from driver to PHYLINK

The DSA drivers that implement .phylink_mac_link_state should normally
register an interrupt for the PCS, from which they should call
phylink_mac_change(). However not all switches implement this, and those
who don't should set this flag in dsa_switch in the .setup callback, so
that PHYLINK will poll for a few ms until the in-band AN link timer
expires and the PCS state settles.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>