lpc_eth: fix tx completion

__lpc_handle_xmit() has two bugs :

1) It can leak skbs in case TXSTATUS_ERROR is set

2) It can wake up txqueue while no slot was freed.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Roland Stigge <stigge@antcom.de>
Tested-by: Roland Stigge <stigge@antcom.de>
Cc: Kevin Wells <kevin.wells@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>