Handle kmod local relocation failures gracefully

It is possible for elf_reloc_local() to fail in the unlikely case of
an unsupported relocation type. If this occurs, do not continue to
process the file.

Reviewed by: kib, markj (earlier version)
MFC after: 1 week
Sponsored by: NetApp, Inc.
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D26701