net: phy: dp83867: w/a for fld detect threshold bootstrapping issue

When the DP83867 PHY is strapped to enable Fast Link Drop (FLD) feature
STRAP_STS2.STRAP_ FLD (reg 0x006F bit 10), the Energy Lost Threshold for
FLD Energy Lost Mode FLD_THR_CFG.ENERGY_LOST_FLD_THR (reg 0x002e bits 2:0)
will be defaulted to 0x2. This may cause the phy link to be unstable. The
new DP83867 DM recommends to always restore ENERGY_LOST_FLD_THR to 0x1.

Hence, restore default value of FLD_THR_CFG.ENERGY_LOST_FLD_THR to 0x1 when
FLD is enabled by bootstrapping as recommended by DM.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>