net: icplus: fix interrupt mask

This patch fixes the interrupt mask for IC101 A/G devices
and now enables the link/speed/duplex interrupts.
This is done by setting the "INTR pin used" bit and cleaning
all the other bits in the Register 17.

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