It would be kinder to WARN() and recover in several spots here instead
of BUG()ing.

Also, it looks like the read_u32_from_xdr_buf() call could actually
fail, though it might require a broken (or malicious) client, so convert
that to just an error return.
Reported-by: NWeston Andros Adamson <dros@monkey.org>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>