net: hv_netvsc: reject RSS hash key programming without RX indirection table

RSS configuration requires a valid RX indirection table. When the device
reports a single receive queue, rndis_filter_device_add() does not
allocate an indirection table, accepting RSS hash key updates in this
state leads to a hang.

Fix this by gating netvsc_set_rxfh() on ndc->rx_table_sz and return
-EOPNOTSUPP when the table is absent. This aligns set_rxfh with the device
capabilities and prevents incorrect behavior.

Fixes: 962f3fee83a4 ("netvsc: add ethtool ops to get/set RSS key")
Signed-off-by: Aditya Garg <[e-mail]>
Reviewed-by: Dipayaan Roy <[e-mail]>
Reviewed-by: Haiyang Zhang <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/hyperv/netvsc_drv.c

···
 	    rxfh->hfunc != ETH_RSS_HASH_TOP)
 		return -EOPNOTSUPP;
 
+	if (!ndc->rx_table_sz)
+		return -EOPNOTSUPP;
+
 	rndis_dev = ndev->extension;
 	if (rxfh->indir) {
 		for (i = 0; i < ndc->rx_table_sz; i++)