Avoid expensive RFC 3779 checks during cert verification

Avoid expensive RFC 3779 checks during cert verification

X509v3_{addr,asid}_is_canonical() check that the ipAddrBlocks and
autonomousSysIds extension conform to RFC 3779. These checks are not
cheap. Certs containing non-conformant extensions should not be
considered valid, so mark them with EXFLAG_INVALID while caching the
extension information in x509v3_cache_extensions(). This way the
expensive check while walking the chains during X509_verify_cert() is
replaced with a cheap check of the extension flags. This avoids a lot
of superfluous work when validating numerous certs with similar chains
against the same roots as is done in rpki-client.

Issue noticed and fix suggested by claudio
ok claudio inoguchi jsing