dtls: use dtls_send_handshake_msg_hash() in dtls_verify_peer()
dtls: use dtls_send_handshake_msg_hash() in dtls_verify_peer()

This also makes it possible to give dtls_send_handshake_msg_hash() an
own session struct and make it then work with peer == NULL.

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

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