mlxsw: spectrum_ipip: Fix memory leak when changing remote IPv6 address

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

mlxsw: spectrum_ipip: Fix memory leak when changing remote IPv6 address

The device stores IPv6 addresses that are used for encapsulation in
linear memory that is managed by the driver.

Changing the remote address of an ip6gre net device never worked
properly, but since cited commit the following reproducer [1] would
result in a warning [2] and a memory leak [3]. The problem is that the
new remote address is never added by the driver to its hash table (and
therefore the device) and the old address is never removed from it.

Fix by programming the new address when the configuration of the ip6gre
net device changes and removing the old one. If the address did not
change, then the above would result in increasing the reference count of
the address and then decreasing it.

[1]
# ip link add name bla up type ip6gre local 2001:db8:1::1 remote 2001:db8:2::1 tos inherit ttl inherit
# ip link set dev bla type ip6gre remote 2001:db8:3::1
# ip link del dev bla
# devlink dev reload pci/0000:01:00.0

[2]
WARNING: CPU: 0 PID: 1682 at drivers/net/ethernet/mellanox/mlxsw/spectrum.c:3002 mlxsw_sp_ipv6_addr_put+0x140/0x1d0
Modules linked in:
CPU: 0 UID: 0 PID: 1682 Comm: ip Not tainted 6.12.0-rc3-custom-g86b5b55bc835 #151
Hardware name: Nvidia SN5600/VMOD0013, BIOS 5.13 05/31/2023
RIP: 0010:mlxsw_sp_ipv6_addr_put+0x140/0x1d0
[...]
Call Trace:
<TASK>
mlxsw_sp_router_netdevice_event+0x55f/0x1240
notifier_call_chain+0x5a/0xd0
call_netdevice_notifiers_info+0x39/0x90
unregister_netdevice_many_notify+0x63e/0x9d0
rtnl_dellink+0x16b/0x3a0
rtnetlink_rcv_msg+0x142/0x3f0
netlink_rcv_skb+0x50/0x100
netlink_unicast+0x242/0x390
netlink_sendmsg+0x1de/0x420
____sys_sendmsg+0x2bd/0x320
___sys_sendmsg+0x9a/0xe0
__sys_sendmsg+0x7a/0xd0
do_syscall_64+0x9e/0x1a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f

[3]
unreferenced object 0xffff898081f597a0 (size 32):
comm "ip", pid 1626, jiffies 4294719324
hex dump (first 32 bytes):
20 01 0d b8 00 02 00 00 00 00 00 00 00 00 00 01 ...............
21 49 61 83 80 89 ff ff 00 00 00 00 01 00 00 00 !Ia.............
backtrace (crc fd9be911):
[<00000000df89c55d>] __kmalloc_cache_noprof+0x1da/0x260
[<00000000ff2a1ddb>] mlxsw_sp_ipv6_addr_kvdl_index_get+0x281/0x340
[<000000009ddd445d>] mlxsw_sp_router_netdevice_event+0x47b/0x1240
[<00000000743e7757>] notifier_call_chain+0x5a/0xd0
[<000000007c7b9e13>] call_netdevice_notifiers_info+0x39/0x90
[<000000002509645d>] register_netdevice+0x5f7/0x7a0
[<00000000c2e7d2a9>] ip6gre_newlink_common.isra.0+0x65/0x130
[<0000000087cd6d8d>] ip6gre_newlink+0x72/0x120
[<000000004df7c7cc>] rtnl_newlink+0x471/0xa20
[<0000000057ed632a>] rtnetlink_rcv_msg+0x142/0x3f0
[<0000000032e0d5b5>] netlink_rcv_skb+0x50/0x100
[<00000000908bca63>] netlink_unicast+0x242/0x390
[<00000000cdbe1c87>] netlink_sendmsg+0x1de/0x420
[<0000000011db153e>] ____sys_sendmsg+0x2bd/0x320
[<000000003b6d53eb>] ___sys_sendmsg+0x9a/0xe0
[<00000000cae27c62>] __sys_sendmsg+0x7a/0xd0