selinux: genheaders should fail if too many permissions are defined

Ensure that genheaders fails with an error if too many permissions
are defined in a class to fit within an access vector. This is similar
to a check performed by checkpolicy when compiling the policy.

Also, fix the suffix on the permission constants generated by this program.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>