ENGR00223533 - FEC : fix net watchdog timeout due not refreshing TX timers

ENGR00223533 - FEC : fix net watchdog timeout due not refreshing TX timers

When do overnight gpu stress test throught nfs, kernel dump as below:

------------[ cut here ]------------
WARNING: at net/sched/sch_generic.c:255 dev_watchdog+0x284/0x2a8()
NETDEV WATCHDOG: eth0 (fec): transmit queue 0 timed out
Modules linked in: galcore imx2_wd_test [last unloaded: galcore]
[<80045854>] (unwind_backtrace+0x0/0xf8) from [<80070c2c>]
(warn_slowpath_common+0x4c/0x64)
<snip>

In sometime, ethernet cannot recover after watchdog timeout which
results in nfs no responding and system hang on.

The patch fixes the way that ->trans_start is refreshed to avoid watchdog
timeout during ethernet status change (such as speed, duplex), and re-init
fec to recover ethernet after watchdog timeout.

Signed-off-by: Fugang Duan  <B38611@freescale.com>