l3mdev: l3mdev_master_upper_ifindex_by_index_rcu should be using netdev_master_upper_dev_get_rcu

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]...