phy: micrel: Ensure interrupts are reenabled on resume

At least on ksz8081, when getting back from power down, interrupts are
disabled. ensure they are reenabled if they were previously enabled.

This fixes resuming which is failing on the xplained boards from atmel
since 321beec5 (net: phy: Use interrupts when available in NOLINK
state)

Fixes: 321beec5

 (net: phy: Use interrupts when available in NOLINK state)
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>