[SERMOUSE]: Sun mice speak 5-byte protocol too.

Noticed by Christophe Zimmerman, this explains the slow mouse movement
with 2.6.x kernels.

And checking the 2.4.x drivers/sbus/char/sunmouse.c driver shows we
always used a 5-byte protocol with Sun mice in the past.  I have no
idea how the 3-byte thing got into the 2.6.x driver, but it's surely
wrong.

Signed-off-by: David S. Miller <davem@davemloft.net>