alx: Reset phy speed after resume

This fixes bug 62491 (https://bugzilla.kernel.org/show_bug.cgi?id=62491

).
After resuming some users got the following error flooding the kernel log:
alx 0000:02:00.0: invalid PHY speed/duplex: 0xffff

Signed-off-by: Jonas Hahnfeld <linux@hahnjo.de>
Signed-off-by: David S. Miller <davem@davemloft.net>