tls/ccm8: reduce the cipher strength for CCM8 ciphers to 64 bits

tls/ccm8: reduce the cipher strength for CCM8 ciphers to 64 bits

This is the length of the tag they use and should be considered an upper bound
on their strength.

This lowers their security strength to level 0.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16652)