stmmac: enable wol via magic frame by default.

This patch enables it by default when the driver starts.
This has been required by many people and seems to actually be
useful on STB.
At any rate, the WoL modes can be selected and turned-on/off
by using the ethtool at run-time by users.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>