Use service-provider-ca.pem instead of root-ca.pem.

According to DLNA X.509 CVP-2 Certificate Specification v0.2:

> A CVP-2 Client should use the DTLA CVP‐2 Service Provider CA Certificate
> (defined in DTLA CVP-2) to verify that an X.509 certificate is an X.509
> CVP-2 Certificate. The DTLA Root CA Certificate shall not be used as this
> may be the root of certificates used for other purposes.