net: mvpp2: increase the number of s/w threads to 9

This patch sets the number of s/w threads to 9, its maximum value,
instead of 8. This is not a fix as only 4 of the s/w threads were used
so far, but more could be used in the future.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>