Next patch uses l3mdev_master_upper_ifindex_by_index_rcu which throws
a splat with debug kernels:

[13783.087570] ------------[ cut here ]------------
[13783.093974] RTNL: assertion failed at net/core/dev.c (6702)
[13783.100761] WARNING: CPU: 3 PID: 51132 at net/core/dev.c:6702 netdev_master_upper_dev_get+0x16a/0x1a0

[13783.184226] CPU: 3 PID: 51132 Comm: kworker/3:3 Not tainted 5.17.0-custom-100090-g6f963aafb1cc #682
[13783.194788] Hardware name: Mellanox Technologies Ltd. MSN2010/SA002610, BIOS 5.6.5 08/24/2017
[13783.204755] Workqueue: mld mld_ifc_work [ipv6]
[13783.210338] RIP: 0010:netdev_master_upper_dev_get+0x16a/0x1a0
[13783.217209] Code: 0f 85 e3 fe ff ff e8 65 ac ec fe ba 2e 1a 00 00 48 c7 c6 60 6f 38 83 48 c7 c7 c0 70 38 83 c6 05 5e b5 d7 01 01 e8 c6 29 52 00 <0f> 0b e9 b8 fe ff ff e8 5a 6c 35 ff e9 1c ff ff ff 48 89 ef e8 7d
[13783.238659] RSP: 0018:ffffc9000b37f5a8 EFLAGS: 00010286
[13783.244995] RAX: 0000000000000000 RBX: ffff88812ee5c000 RCX: 0000000000000000
[13783.253379] RDX: ffff88811ce09d40 RSI: ffffffff812d0fcd RDI: fffff5200166fea7
[13783.261769] RBP: 0000000000000000 R08: 0000000000000001 R09: ffff8882375f4287
[13783.270138] R10: ffffed1046ebe850 R11: 0000000000000001 R12: dffffc0000000000
[13783.278510] R13: 0000000000000275 R14: ffffc9000b37f688 R15: ffff8881273b4af8
[13783.286870] FS:  0000000000000000(0000) GS:ffff888237400000(0000) knlGS:0000000000000000
[13783.296352] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[13783.303177] CR2: 00007ff25fc9b2e8 CR3: 0000000174d23000 CR4: 00000000001006e0
[13783.311546] Call Trace:
[13783.314660]  <TASK>
[13783.317553]  l3mdev_master_upper_ifindex_by_index_rcu+0x43/0xe0
...

Change l3mdev_master_upper_ifindex_by_index_rcu to use
netdev_master_upper_dev_get_rcu.

Fixes: 6a6d6681 ("l3mdev: add function to retreive upper master")
Signed-off-by: Ido Schimmel <idosch@idosch.org>
Signed-off-by: David Ahern <dsahern@kernel.org>
Cc: Alexis Bauvin <abauvin@scaleway.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>