[MIPS] IP27: startup_bridge_irq: connect interrupt.

shutdown_bridge_irq disconnects the irq so we need to connect the irq or
requesting the same irq a send time will fail.  This used to make
things like ifconfig eth0 down; ifconfig eth0 up fail on IP27.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>