mlxsw: spectrum_buffers: Fix memory corruptions on Spectrum-4 systems

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

mlxsw: spectrum_buffers: Fix memory corruptions on Spectrum-4 systems

The following two shared buffer operations make use of the Shared Buffer
Status Register (SBSR):

# devlink sb occupancy snapshot pci/0000:01:00.0
# devlink sb occupancy clearmax pci/0000:01:00.0

The register has two masks of 256 bits to denote on which ingress /
egress ports the register should operate on. Spectrum-4 has more than
256 ports, so the register was extended by cited commit with a new
'port_page' field.

However, when filling the register's payload, the driver specifies the
ports as absolute numbers and not relative to the first port of the port
page, resulting in memory corruptions [1].

Fix by specifying the ports relative to the first port of the port page.

[1]
BUG: KASAN: slab-use-after-free in mlxsw_sp_sb_occ_snapshot+0xb6d/0xbc0
Read of size 1 at addr ffff8881068cb00f by task devlink/1566
[...]
Call Trace:
<TASK>
dump_stack_lvl+0xc6/0x120
print_report+0xce/0x670
kasan_report+0xd7/0x110
mlxsw_sp_sb_occ_snapshot+0xb6d/0xbc0
mlxsw_devlink_sb_occ_snapshot+0x75/0xb0
devlink_nl_sb_occ_snapshot_doit+0x1f9/0x2a0
genl_family_rcv_msg_doit+0x20c/0x300
genl_rcv_msg+0x567/0x800
netlink_rcv_skb+0x170/0x450
genl_rcv+0x2d/0x40
netlink_unicast+0x547/0x830
netlink_sendmsg+0x8d4/0xdb0
__sys_sendto+0x49b/0x510
__x64_sys_sendto+0xe5/0x1c0
do_syscall_64+0xc1/0x1d0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
[...]
Allocated by task 1:
kasan_save_stack+0x33/0x60
kasan_save_track+0x14/0x30
__kasan_kmalloc+0x8f/0xa0
copy_verifier_state+0xbc2/0xfb0
do_check_common+0x2c51/0xc7e0
bpf_check+0x5107/0x9960
bpf_prog_load+0xf0e/0x2690
__sys_bpf+0x1a61/0x49d0
__x64_sys_bpf+0x7d/0xc0
do_syscall_64+0xc1/0x1d0
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 1:
kasan_save_stack+0x33/0x60
kasan_save_track+0x14/0x30
kasan_save_free_info+0x3b/0x60
poison_slab_object+0x109/0x170
__kasan_slab_free+0x14/0x30
kfree+0xca/0x2b0
free_verifier_state+0xce/0x270
do_check_common+0x4828/0xc7e0
bpf_check+0x5107/0x9960
bpf_prog_load+0xf0e/0x2690
__sys_bpf+0x1a61/0x49d0
__x64_sys_bpf+0x7d/0xc0
do_syscall_64+0xc1/0x1d0
entry_SYSCALL_64_after_hwframe+0x77/0x7f