selftests: drv-net: rss_ctx: fix the queue count check

selftests: drv-net: rss_ctx: fix the queue count check

Commit 0d6ccfe6b319 ("selftests: drv-net: rss_ctx: check for all-zero keys")
added a skip exception if NIC has fewer than 3 queues enabled,
but it's just constructing the object, it's not actually rising
this exception.

Before:

  # Exception| net.lib.py.utils.CmdExitFailure: Command failed: ethtool -X enp1s0 equal 3 hkey d1:cc:77:47:9d:ea:15:f2:b9:6c:ef:68:62:c0:45:d5:b0:99:7d:cf:29:53:40:06:3d:8e:b9:bc:d4:70:89:b8:8d:59:04:ea:a9:c2:21:b3:55:b8:ab:6b:d9:48:b4:bd:4c:ff:a5:f0:a8:c2
  not ok 1 rss_ctx.test_rss_key_indir

After:

  ok 1 rss_ctx.test_rss_key_indir # SKIP Device has fewer than 3 queues (or doesn't support queue stats)

Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250827173558.3259072-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>