[IRDA]: irda-usb bug fixes

This patch fixes 2 bugs in the USB-IrDA code.

The first one is a buffer overrun in the RX path. We are now using
IRDA_SKB_MAX_MTU when initializing the Rx URB.

The second one is a potential stack recursion when unplugging the USB
dongle.  It seems that first we get the Rx URB with a generic error
code, and after a while the Rx URB comes again with a "disconnect"
error code.  Since we are resubmitting the Rx URB immediately after
receiving the first error one, we might enter an endless loop.

When getting an error Rx URB, the patch defers the Rx URB resubmitting
so that it gives us a chance to catch the disconnect one, in case the
dongle has juts been unplugged.

Tested against 2.6.16-rc2.

Patch from Jean Tourrilhes

Signed-off-by: Jean Tourrilhes <jt@hpl.hp.com>
Signed-off-by: Samuel Ortiz <samuel.ortiz@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>