Do not encode more than CTF_MAX_VLEN(1023) enum members.

Do not encode more than CTF_MAX_VLEN(1023) enum members.

CTF can not represent enums with more than CTF_MAX_VLEN members, but
ctfconvert will happily ignore that limitation and create CTF section no
other tool can interpret.

This change is different from similar change from upstream, which just
returns an error if big enum is encountered.  Doing that means that
every FreeBSD kernel with compiled in hwpmc will have no useable CTF
information due to pmc_event enum having 1236+ members.