tinydtls: add new function to send the ClientHello
tinydtls: add new function to send the ClientHello

Instead of having the code for sending the ClientHello without cookie
in dtls_connect() and with a cookie in check_server_hello() use one
function dtls_send_client_hello(), which can handle both cases and is
called by the other functions.

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

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