more fixes for Contiki 2.7
more fixes for Contiki 2.7

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