sfc: make coding style of PTP addresses consistent with core

Follow the style used in the core kernel (e.g.
include/linux/etherdevice.h and include/linux/in6.h) for the PTP IPv6
and Ethernet addresses. No functional changes.

Signed-off-by: Alex Austin <alex.austin@amd.com>
Reviewed-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>