net/netlink: Correct the comment on netlink message max cap

Since commit d35c99ff ("netlink: do not enter direct reclaim from
netlink_dump()") the cap is 32KiB.

Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com>
Link: https://patch.msgid.link/20241113-tcp-md5-diag-prep-v2-5-00a2a7feb1fa@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>