Endianness fixes

- rtl8169_rx_csum() forgot to convert the descriptor to cpu order,
- same thing for rtl8169_rx_vlan_skb() but this one is more tricky as
  the layout of the (u32) word in the 8169 descriptor calls for a
  second level of swap at the vlan tag level (u16). The old code only
  did the second part (in an endian-dependant way, how fun).
- rtl8169_tx_vlan_tag(): this time the (u32 descriptor level) cpu_to_le32
  is issued in rtl8169_start_xmit but the (u16 vlan tag level) cpu_to_be16
  is not right any more.

Summary: avoid even calls to cpu_to_{b/l}eXX on a given piece of data.

The change has no effect on x86. Now sparc64 talks to x86.
Pinpointed-by: Jon Mason <jdmason@us.ibm.com>
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>