DTLS fixes for signed/unsigned issues

Reviewed-by: Emilia Käsper <emilia@openssl.org>
(cherry picked from commit 1904d21123849a65dafde1705e6dd5b7c2f420eb)
Remove extraneous white space, and add some braces

Reviewed-by: Emilia Käsper <emilia@openssl.org>
(cherry picked from commit 55e530265a7ea8f264717a4e37338cc04eca2007)