Fix ssl socket resend

[artygus]

Set 2 flags for ssl connection:

• SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER needed to properly support sm_resend, since buffer gets copied to new location for retries
• SSL_MODE_ENABLE_PARTIAL_WRITE writes message in ~16kb chunks, which is more in line with current non-blocking architecture (basically imitates the behaviour of write())

Fixes #344