BUG/MEDIUM: ssl: Don't call ssl_sock_io_cb() directly.

BUG/MEDIUM: ssl: Don't call ssl_sock_io_cb() directly.

In the SSL code, when we were waiting for the availability of the crypto
engine, once it is ready and its fd's I/O handler is called, don't call
ssl_sock_io_cb() directly, instead, call tasklet_wakeup() on the
ssl_sock_ctx's tasklet. We were calling ssl_sock_io_cb() with NULL as
a tasklet, which used to be fine, but it is no longer true since the
fd takeover changes. We could just provide the tasklet, but let's just
wake the tasklet, as is done for other FDs, for fairness.

This should fix github issue #856.

This should be backported into 2.2.