net: phylink: fix ethtool -A with attached PHYs

Fix a phylink's ethtool set_pauseparam support deadlock caused by phylib
interacting with phylink: we must not hold the state lock while calling
phylib functions that may call into phylink_phy_change().

Fixes: f904f15e ("net: phylink: allow ethtool -A to change flow control advertisement")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>