mlx4_en: Only cycle port if HW timestamp config changes

mlx4_en: Only cycle port if HW timestamp config changes

If the hwtstamp_config matches what is currently set for the device then
simply return.  Without this change any program that tries to enable
hardware timestamps will cause the link to cycle even if hardware
timstamps were already enabled.

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Acked-By: Hadar Hen Zion <hadarh@mellanox.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>