net: phy: phylink: fix SFP interface autodetection

When connecting SFP PHY to phylink use the detected interface.
Otherwise, the link fails to come up when the configured 'phy-mode'
differs from the SFP detected mode.

Move most of phylink_connect_phy() into __phylink_connect_phy(), and
leave phylink_connect_phy() as a wrapper. phylink_sfp_connect_phy() can
now pass the SFP detected PHY interface to __phylink_connect_phy().

This fixes 1GB SFP module link up on eth3 of the Macchiatobin board that
is configured in the DT to "2500base-x" phy-mode.

Fixes: 9525ae83 ("phylink: add phylink infrastructure")
Suggested-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>