m32r: Fix ei_tx_timeout() in drivers/net/lib8390.c

Change INT0 trigger mode from edge-sense mode to level-sense mode,
in order to fix the following timeout error:
  'NETDEV WATCHDOG: eth0: transmit timed out'.

This patch is required only for the Mappi platform.

Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Cc: Hitoshi Yamamoto <hitoshiy@linux-m32r.org>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>