net: mana: hardening: Reject zero max_num_queues from GDMA_QUERY_MAX_RESOURCES

In a CVM environment, hardware responses cannot be trusted. The
GDMA_QUERY_MAX_RESOURCES command returns resource limits used to
determine the maximum number of queues.

In mana_gd_query_max_resources(), gc->max_num_queues is initialized
from num_online_cpus() and successively clamped by the hardware-reported
max_eq, max_cq, max_sq, max_rq, and num_msix_usable values. If any of
these hardware values is zero, gc->max_num_queues becomes zero and the
function returns success. This leads to a confusing failure later when
alloc_etherdev_mq() is called with zero queues, returning NULL and
producing a misleading -ENOMEM error.

Add an explicit zero check for gc->max_num_queues after all clamping
steps and return -ENOSPC for a clear early failure, consistent with the
existing gc->num_msix_usable <= 1 guard.

Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Reviewed-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
Link: https://patch.msgid.link/20260430083627.1873757-1-ernis@linux.microsoft.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microsoft/mana/gdma_main.c

@@ -194,6 +194,9 @@ static int mana_gd_query_max_resources(struct pci_dev *pdev)
 	if (gc->max_num_queues > gc->num_msix_usable - 1)
 		gc->max_num_queues = gc->num_msix_usable - 1;
 
+	if (gc->max_num_queues == 0)
+		return -ENOSPC;
+
 	return 0;
 }