r8169: mac address change support

Merged from Realtek's r8169-6.001 driver.

I have added some locking to protect against the arp monitoring
timer in the bonding driver. Accessing the configuration registers
is otherwise performed under RTNL locking.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>