3c59x: Fix bad offset spec in skb_frag_dma_map

Recently aded the use of skb_frag_dma_map to 3c59x, but didn't realize it
automatically included the frag_offset internally, as well as provided an option
to specify an extra offset in the parameter list.  We need to specify an offset
of 0 in the parameter list to avoid skb corruption that results in lost
connections.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Linux Kernel list <linux-kernel@vger.kernel.org>
CC: "David S. Miller" <davem@davemloft.net>
CC: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>