tinydtls.h: include dtls_config.h in tinydtls.h

Fixes dtls_config.h not visible in headers
Include dtls_config.h in tinydtls.h and include tinydtls.h in all necessary
headers.

Remaining headers do not use 'ifdef', but they may require it too.

Change-Id: I39c86dffc8bbc8bd7551e74386994f92f49d00ec
Signed-off-by: Gaëtan Harter <gaetan.harter@inria.fr>
17 files changed