net: stmmac: Fix reception of Broadcom switches tags

Broadcom tags inserted by Broadcom switches put a 4 byte header after
the MAC SA and before the EtherType, which may look like some sort of 0
length LLC/SNAP packet (tcpdump and wireshark do think that way). With
ACS enabled in stmmac the packets were truncated to 8 bytes on
reception, whereas clearing this bit allowed normal reception to occur.

In order to make that possible, we need to pass a net_device argument to
the different core_init() functions and we are dependent on the Broadcom
tagger padding packets correctly (which it now does). To be as little
invasive as possible, this is only done for gmac1000 when the network
device is DSA-enabled (netdev_uses_dsa() returns true).

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>