ibmveth: Fix endian issues with MAC addresses

The code to load a MAC address into a u64 for passing to the
hypervisor via a register is broken on little endian.

Create a helper function called ibmveth_encode_mac_addr
which does the right thing in both big and little endian.

We were storing the MAC address in a long in struct ibmveth_adapter.
It's never used so remove it - we don't need another place in the
driver where we create endian issues with MAC addresses.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: stable@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>