net: mvneta: Prevent out of bounds read in mvneta_config_rss()

The pp->indir[0] value comes from the user.  It is passed to:

	if (cpu_online(pp->rxq_def))

inside the mvneta_percpu_elect() function.  It needs bounds checkeding
to ensure that it is not beyond the end of the cpu bitmap.

Fixes: cad5d847 ("net: mvneta: Fix the CPU choice in mvneta_percpu_elect")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>