kernel: bump 6.18 to 6.18.39

kernel: bump 6.18 to 6.18.39

Changelog: https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.18.39

Removed upstreamed:
  backport-6.18/704-v7.2-netfilter-flowtable-fix-offloaded-ct-timeout-never-b.patch[1]

All other patches automatically rebased via update_kernel.sh

1. https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v6.18.39&id=81a5971cbe18b474b49c651e32f2194b2fb171fe

Build system: x86/64
Build-tested: x86/64-glibc
Run-tested: x86/64-glibc

Signed-off-by: John Audia <therealgraysky@proton.me>
Link: https://github.com/openwrt/openwrt/pull/24282
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>