vxlan: Fix memory leaks in error path

In the Linux kernel, the following vulnerability has been resolved:

vxlan: Fix memory leaks in error path

The memory allocated by vxlan_vnigroup_init() is not freed in the error
path, leading to memory leaks [1]. Fix by calling
vxlan_vnigroup_uninit() in the error path.

The leaks can be reproduced by annotating gro_cells_init() with
ALLOW_ERROR_INJECTION() and then running:

# echo "100" > /sys/kernel/debug/fail_function/probability
# echo "1" > /sys/kernel/debug/fail_function/times
# echo "gro_cells_init" > /sys/kernel/debug/fail_function/inject
# printf %#x -12 > /sys/kernel/debug/fail_function/gro_cells_init/retval
# ip link add name vxlan0 type vxlan dstport 4789 external vnifilter
RTNETLINK answers: Cannot allocate memory

[1]
unreferenced object 0xffff88810db84a00 (size 512):
comm "ip", pid 330, jiffies 4295010045 (age 66.016s)
hex dump (first 32 bytes):
f8 d5 76 0e 81 88 ff ff 01 00 00 00 00 00 00 02 ..v.............
03 00 04 00 48 00 00 00 00 00 00 01 04 00 01 00 ....H...........
backtrace:
[<ffffffff81a3097a>] kmalloc_trace+0x2a/0x60
[<ffffffff82f049fc>] vxlan_vnigroup_init+0x4c/0x160
[<ffffffff82ecd69e>] vxlan_init+0x1ae/0x280
[<ffffffff836858ca>] register_netdevice+0x57a/0x16d0
[<ffffffff82ef67b7>] __vxlan_dev_create+0x7c7/0xa50
[<ffffffff82ef6ce6>] vxlan_newlink+0xd6/0x130
[<ffffffff836d02ab>] __rtnl_newlink+0x112b/0x18a0
[<ffffffff836d0a8c>] rtnl_newlink+0x6c/0xa0
[<ffffffff836c0ddf>] rtnetlink_rcv_msg+0x43f/0xd40
[<ffffffff83908ce0>] netlink_rcv_skb+0x170/0x440
[<ffffffff839066af>] netlink_unicast+0x53f/0x810
[<ffffffff839072d8>] netlink_sendmsg+0x958/0xe70
[<ffffffff835c319f>] ____sys_sendmsg+0x78f/0xa90
[<ffffffff835cd6da>] ___sys_sendmsg+0x13a/0x1e0
[<ffffffff835cd94c>] __sys_sendmsg+0x11c/0x1f0
[<ffffffff8424da78>] do_syscall_64+0x38/0x80
unreferenced object 0xffff88810e76d5f8 (size 192):
comm "ip", pid 330, jiffies 4295010045 (age 66.016s)
hex dump (first 32 bytes):
04 00 00 00 00 00 00 00 db e1 4f e7 00 00 00 00 ..........O.....
08 d6 76 0e 81 88 ff ff 08 d6 76 0e 81 88 ff ff ..v.......v.....
backtrace:
[<ffffffff81a3162e>] __kmalloc_node+0x4e/0x90
[<ffffffff81a0e166>] kvmalloc_node+0xa6/0x1f0
[<ffffffff8276e1a3>] bucket_table_alloc.isra.0+0x83/0x460
[<ffffffff8276f18b>] rhashtable_init+0x43b/0x7c0
[<ffffffff82f04a1c>] vxlan_vnigroup_init+0x6c/0x160
[<ffffffff82ecd69e>] vxlan_init+0x1ae/0x280
[<ffffffff836858ca>] register_netdevice+0x57a/0x16d0
[<ffffffff82ef67b7>] __vxlan_dev_create+0x7c7/0xa50
[<ffffffff82ef6ce6>] vxlan_newlink+0xd6/0x130
[<ffffffff836d02ab>] __rtnl_newlink+0x112b/0x18a0
[<ffffffff836d0a8c>] rtnl_newlink+0x6c/0xa0
[<ffffffff836c0ddf>] rtnetlink_rcv_msg+0x43f/0xd40
[<ffffffff83908ce0>] netlink_rcv_skb+0x170/0x440
[<ffffffff839066af>] netlink_unicast+0x53f/0x810
[<ffffffff839072d8>] netlink_sendmsg+0x958/0xe70
[<ffffffff835c319f>] ____sys_sendmsg+0x78f/0xa90