kernel: fix missing dependency in 4.14.108
The 4.14.108 bump introduced a missing dependency when building
specific netfilters.
Thsi was not seen as the error does not occur on all targets.
Thanks to Jo-Philipp Wich for providing the fix
Fixes: af6c86dbe56e ("kernel: bump 4.14 to 4.14.108")
Signed-off-by: Koen Vandeputte <[email protected]>