Two cases for not updating active sockets[] with file descriptors from a
session (non epoll code)
coap_retransmit() can release a session
coap_dtls_handle_timeout() can disconnect a session
Move the restransmit test code to before any updates to socket[].
Update coap_dtls_handle_timeout() to return a value indicating a DTLS timeout
has occurred. At the same time move the coap_dtls_handle_timeout() checks
into the first sessions iteration loop, removing having to iterate through the
sessions twice if DTLS.
Jon Shallow
21fd838dc7