There were two problems how tcp_send_direct() was used:
1. The tcp_send_direct() can return ISC_R_CANCELED (or translated error
from uv_tcp_send()), but the isc__nm_async_tcpsend() wasn't checking
the error code and not releasing the uvreq in case of an error.
2. In isc__nm_tcp_send(), when the TCP send is already in the right
netthread, it uses tcp_send_direct() to send the TCP packet right
away. When that happened the uvreq was not freed, and the error code
was returned to the caller. We need to return ISC_R_SUCCESS and
rather use the callback to report an error in such case.
(cherry picked from commit 6af08d1ca6)
Ondřej SurýandEvan Hunt
5547657bce