Clarify the terminology in the noisy dgram BIO

The previous terminology was quite confusing. We try to use drop, duplicate
and delay more consistently and introduce the "reinject" terminology as a
mechanism for implementing duplicates and delays.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22157)