r8169: corrupted IP fragments fix for large mtu.

r8169: corrupted IP fragments fix for large mtu.

[ Upstream commit 9c5028e9da1255dd2b99762d8627b88b29f68cce ]

Noticed with the 8168d (-vb-gr, aka RTL_GIGA_MAC_VER_26).

ConfigX registers should only be written while the Config9346 lock
is held.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Reported-by: Nick Bowler <nbowler@elliptictech.com>
Cc: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>