@SECLEVEL=1 in the cipher string does not reliably lower the security
level for DTLS_METHOD contexts across all pyOpenSSL/OpenSSL builds.
Instead, explicitly allow error 66 (X509_V_ERR_CA_MD_TOO_WEAK) in the
verify callback. This is the error OpenSSL emits when a CA certificate
uses SHA-1 — which Samsung's OCF Root CA does. All other verification
errors (chain trust, expiry, key usage, revocation) are still enforced.