r8169: set TxConfig register after TX / RX is enabled, just like RxConfig

r8169: set TxConfig register after TX / RX is enabled, just like RxConfig

Commit 3559d81e76bf ("r8169: simplify rtl_hw_start_8169") changed order of
two register writes:
1) Caused RxConfig to be written before TX / RX is enabled,
2) Caused TxConfig to be written before TX / RX is enabled.

At least on XIDs 10000000 ("RTL8169sb/8110sb") and
18000000 ("RTL8169sc/8110sc") such writes are ignored by the chip, leaving
values in these registers intact.

Change 1) was reverted by
commit 05212ba8132b42 ("r8169: set RxConfig after tx/rx is enabled for RTL8169sb/8110sb devices"),
however change 2) wasn't.

In practice, this caused TxConfig's "InterFrameGap time" and "Max DMA Burst
Size per Tx DMA Burst" bits to be zero dramatically reducing TX performance
(in my tests it dropped from around 500Mbps to around 50Mbps).

This patch fixes the issue by moving TxConfig register write a bit later in
the code so it happens after TX / RX is already enabled.

Fixes: 05212ba8132b42 ("r8169: set RxConfig after tx/rx is enabled for RTL8169sb/8110sb devices")
Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: David S. Miller <davem@davemloft.net>