DTLS: fix bool logic in TLS extension check.

An error message was only returned when none of the expected TLS
extensions was found, now an error message is returned when not all the
expected TLS Extensions was found.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
DTLS: fix error message when no matching TLS cipher was found.

tinydtls wrote that the ClientHello was too short when no matching
cipher suite was found, this was wrong.

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