dtls: make it possible to send a CCS in a different epoch
dtls: make it possible to send a CCS in a different epoch

We have to send the ChangeCipherSpec with the old cipher, but the
server should only send it after he received the Finish message
encrypted with the new cipher from the client. This makes it possible
to use the a different than the default cipher for CCS.

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

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