ixgbe: Only set gso_type to SKB_GSO_TCPV4 as RSC does not support IPv6

The original fix that was applied for setting gso_type required more change
than necessary because it was assumed ixgbe does RSC on IPv6 frames and this
is not correct.  RSC is only supported with IPv4/TCP frames only.  As such we
can simplify the fix and avoid the unnecessary move of eth_type_trans.

The previous patch "ixgbe: fix gso type" and this patch reduce the entire fix
to one line that sets gso_type to TCPV4 if the frame is RSC.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>