net: sparx5: Move ifh from port to local variable

Currently the ifh is not changed, it is fixed for each frame for each
port that is sent out. Move this on the stack because this ifh needs to
be change based on the frames that are send out. This is needed for PTP
frames.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>