Remove MBEDTLS_SSL_MAX_CONTENT_LEN

[chris-jones-arm]

Context

The configuration option MBEDTLS_SSL_MAX_CONTENT_LEN controls the "Maximum length of incoming and outgoing plaintext fragments". Since its introduction two more finer-grained options have been introduced: MBEDTLS_SSL_IN_CONTENT_LEN and MBEDTLS_SSL_OUT_CONTENT_LEN. These two options provide exactly the same functionality as MBEDTLS_SSL_MAX_CONTENT_LEN however allow for more control over the input and output separately.

---

Rationale

As there are already two other config options which together provide the same functionality as MBEDTLS_SSL_MAX_CONTENT_LEN it makes sense to remove it in favour of the using the other options. Having redundant config options only leads to more chance to misconfigure and misunderstand how the options should be used to provide the desired result.

This option was previously kept to preserve API compatibility but with Mbed TLS 3.0 we no longer have that requirement and so this can now be removed from 3.0 onwards.

---

Work items for 3.0

• Remove the option MBEDTLS_SSL_MAX_CONTENT_LEN from config.h.
• Replace references to MBEDTLS_SSL_MAX_CONTENT_LEN with appropriate references to the relevant option: MBEDTLS_SSL_IN_CONTENT_LEN or MBEDTLS_SSL_OUT_CONTENT_LEN.