As a single thread can process only one TCP send at the time, we don't
really need a memory pool for the TCP buffers, but it's enough to have
a single per-loop (client manager) static buffer that's being used to
assemble the DNS message and then it gets copied into own sending
buffer.
In the future, this should get optimized by exposing the uv_try API
from the network manager, and first try to send the message directly
and allocate the sending buffer only if we need to send the data
asynchronously.
(cherry picked from commit 297cc840fbaf34b9dfa1d02d88a023cd5bf5dc4a)
Ondřej SurýandNicki Křížek
3f6b7f57a6