Feature Request: set SSL max fragment size

[everslick]

I have seen that mosquitto got support for openssl 1.1.0 recently. as far as I understand this would also allow to limit the maximum fragment size sent on TLS connections. the required API function in openssl is SSL_CTX_set_max_send_fragment(). I guess this would also require a new configuration setting. if it would be feasible to set it depending on the client prefix i cannot say. A global limit would be already of great help for ram constrained devices.

what do others think about the usefulness of this feature?