dtls: use ret variable name instead of i
dtls: use ret variable name instead of i

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

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