openafsClient: mark as broken on unsupported kernels

Sandboxed builds against linux 3.14 and 4.4 fail; 3.18.29 and 4.3
succeed.  From this, I conclude that 4.3 is the latest supported
version, while the lower bound is set to the oldest kernel in
nixpkgs >3.14 (the changelog does not indicate otherwise).

It appears that openafs-client is simply incompatible with grsec;
all hydra builds of openafs-client on grsec fail; local sandboxed
builds against grsec with the most recent openafs-client also fail.