net: mvpp2: do not disable GMAC padding

Short fragmented packets may never be sent by the hardware when padding
is disabled. This patch stop modifying the GMAC padding bits, to leave
them to their reset value (disabled).

Fixes: 3919357f

 ("net: mvpp2: initialize the GMAC when using a port")
Signed-off-by: Yan Markman <ymarkman@marvell.com>
[Antoine: commit message]
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>