vxge: add receive hardware timestamping

Add support for enable/disabling hardware timestamping on receive
packets via ioctl call.  When enabled, the hardware timestamp replaces
the FCS in the payload.

Signed-off-by: Jon Mason <jon.mason@exar.com>
Signed-off-by: Ram Vepa <ram.vepa@exar.com>
Signed-off-by: David S. Miller <davem@davemloft.net>