net: bcmgenet: improve TX timeout

Dump useful ring statistics along with interrupt status, software
maintained pointers and hardware registers to help troubleshoot TX queue
stalls.

When a timeout occurs, disable TX NAPI for the rings, dump their states
while interrupts are disabled, re-enable interrupts, NAPI and queue flow
control to help with the recovery.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>