net/mlx5e: Use ipv6_stub to avoid dependency with ipv6 being a module

mlx5 is dependent on IPv6 tristate since we use ipv6's nd_tbl directly,
alternatively we can use ipv6_stub->nd_tbl and remove the dependency.
Reported-by: Walter Harms <wharms@bfs.de>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/Kconfig

@@ -33,7 +33,6 @@ config MLX5_FPGA
 config MLX5_CORE_EN
 	bool "Mellanox 5th generation network adapters (ConnectX series) Ethernet support"
 	depends on NETDEVICES && ETHERNET && INET && PCI && MLX5_CORE
-	depends on IPV6=y || IPV6=n || MLX5_CORE=m
 	select PAGE_POOL
 	select DIMLIB
 	default n

drivers/net/ethernet/mellanox/mlx5/core/en_rep.c

@@ -38,6 +38,7 @@
 #include <net/netevent.h>
 #include <net/arp.h>
 #include <net/devlink.h>
+#include <net/ipv6_stubs.h>
 
 #include "eswitch.h"
 #include "en.h"
@@ -499,16 +500,18 @@ void mlx5e_remove_sqs_fwd_rules(struct mlx5e_priv *priv)
 	mlx5e_sqs2vport_stop(esw, rep);
 }
 
+static unsigned long mlx5e_rep_ipv6_interval(void)
+{
+	if (IS_ENABLED(CONFIG_IPV6) && ipv6_stub->nd_tbl)
+		return NEIGH_VAR(&ipv6_stub->nd_tbl->parms, DELAY_PROBE_TIME);
+
+	return ~0UL;
+}
+
 static void mlx5e_rep_neigh_update_init_interval(struct mlx5e_rep_priv *rpriv)
 {
-#if IS_ENABLED(CONFIG_IPV6)
-	unsigned long ipv6_interval = NEIGH_VAR(&nd_tbl.parms,
-						DELAY_PROBE_TIME);
-#else
-	unsigned long ipv6_interval = ~0UL;
-#endif
-	unsigned long ipv4_interval = NEIGH_VAR(&arp_tbl.parms,
-						DELAY_PROBE_TIME);
+	unsigned long ipv4_interval = NEIGH_VAR(&arp_tbl.parms, DELAY_PROBE_TIME);
+	unsigned long ipv6_interval = mlx5e_rep_ipv6_interval();
 	struct net_device *netdev = rpriv->netdev;
 	struct mlx5e_priv *priv = netdev_priv(netdev);
 
@@ -917,7 +920,7 @@ static int mlx5e_rep_netevent_event(struct notifier_block *nb,
 	case NETEVENT_NEIGH_UPDATE:
 		n = ptr;
 #if IS_ENABLED(CONFIG_IPV6)
-		if (n->tbl != &nd_tbl && n->tbl != &arp_tbl)
+		if (n->tbl != ipv6_stub->nd_tbl && n->tbl != &arp_tbl)
 #else
 		if (n->tbl != &arp_tbl)
 #endif
@@ -944,7 +947,7 @@ static int mlx5e_rep_netevent_event(struct notifier_block *nb,
 		 * done per device delay prob time parameter.
 		 */
 #if IS_ENABLED(CONFIG_IPV6)
-		if (!p->dev || (p->tbl != &nd_tbl && p->tbl != &arp_tbl))
+		if (!p->dev || (p->tbl != ipv6_stub->nd_tbl && p->tbl != &arp_tbl))
 #else
 		if (!p->dev || p->tbl != &arp_tbl)
 #endif

drivers/net/ethernet/mellanox/mlx5/core/en_tc.c

@@ -1492,7 +1492,7 @@ void mlx5e_tc_update_neigh_used_value(struct mlx5e_neigh_hash_entry *nhe)
 		tbl = &arp_tbl;
 #if IS_ENABLED(CONFIG_IPV6)
 	else if (m_neigh->family == AF_INET6)
-		tbl = &nd_tbl;
+		tbl = ipv6_stub->nd_tbl;
 #endif
 	else
 		return;