This allows an application to determine what the built version is
as well as what the runtime version of a TLS library is.
include/coap2/coap_dtls.h
Add built_version to coap_tls_version_t
src/coap_openssl.c
src/coap_tinydtls.c
Additionally populate coap_tls_version_t with build_version when
coap_get_tls_library_version() is called.
src/coap_tinydtls.c
Correct the version returned as actual TinyDTLS version instead the
binary value of a DTLS packet type.