selftests: drv-net: Limit the max number of queues in procfs_downup_hammer

selftests: drv-net: Limit the max number of queues in procfs_downup_hammer

For NICs with a large (1024+) number of queues, this test can cause
excessive memory fragmentation. This results in OOM errors, and in the
worst case driver/kernel crashes. We don't need to test with the max number
of queues, just enough to create a high likelihood of races between
reconfiguration and stats getting read.

Signed-off-by: Dimitri Daskalakis <dimitri.daskalakis1@gmail.com>
Link: https://patch.msgid.link/20251111225319.3019542-1-dimitri.daskalakis1@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>