RDMA/core: Resolve MAC of next-hop device without ARP support

JIRA: https://issues.redhat.com/browse/RHEL-109942

commit 200651b
Author: Parav Pandit <parav@nvidia.com>
Date:   Tue Sep 16 14:11:01 2025 +0300

    RDMA/core: Resolve MAC of next-hop device without ARP support

    Currently, if the next-hop netdevice does not support ARP resolution,
    the destination MAC address is silently set to zero without reporting
    an error. This leads to incorrect behavior and may result in packet
    transmission failures.

    Fix this by deferring MAC resolution to the IP stack via neighbour
    lookup, allowing proper resolution or error reporting as appropriate.

    Fixes: 7025fcd ("IB: address translation to map IP toIB addresses (GIDs)")
    Signed-off-by: Parav Pandit <parav@nvidia.com>
    Reviewed-by: Vlad Dumitrescu <vdumitrescu@nvidia.com>
    Signed-off-by: Edward Srouji <edwards@nvidia.com>
    Link: https://patch.msgid.link/20250916111103.84069-3-edwards@nvidia.com
    Signed-off-by: Leon Romanovsky <leon@kernel.org>

Signed-off-by: Kamal Heib <kheib@redhat.com>

Author: Kamalheib

drivers/infiniband/core/addr.c

@@ -460,14 +460,10 @@ static int addr_resolve_neigh(const struct dst_entry *dst,
 {
 	int ret = 0;
 
-	if (ndev_flags & IFF_LOOPBACK) {
+	if (ndev_flags & IFF_LOOPBACK)
 		memcpy(addr->dst_dev_addr, addr->src_dev_addr, MAX_ADDR_LEN);
-	} else {
-		if (!(ndev_flags & IFF_NOARP)) {
-			/* If the device doesn't do ARP internally */
-			ret = fetch_ha(dst, addr, dst_in, seq);
-		}
-	}
+	else
+		ret = fetch_ha(dst, addr, dst_in, seq);
 	return ret;
 }