dtls: send a CertificateVerify message
dtls: send a CertificateVerify message

This send the client's CertificateVerify message which contains a
signature over the hole handshake till this package.

Signed-off-by: Hauke Mehrtens <435ddd46dc66c007a1fa20144c823d37e0d23436@hauke-m.de>

yunus/TinyDTLS-WebID,fvdnabee/tinydtls,spark/tinydtls,thecodemaiden/tinydtls-fork,fvdnabee/tinydtls,jvermillard/tinydtls,OlegHahm/tinydtls,OlegHahm/tinydtls,nmacs/tinydtls,thecodemaiden/tinydtls-fork,spark/tinydtls,jvermillard/tinydtls,yunus/TinyDTLS-WebID,OlegHahm/tinydtls,yunus/TinyDTLS-WebID,nmacs/tinydtls,thecodemaiden/tinydtls-fork,spark/tinydtls,nmacs/tinydtls,nmacs/tinydtls,jvermillard/tinydtls,fvdnabee/tinydtls