When reading exactly rev->available bytes, rev->available might become 0
after FIONREAD usage introduction in efd71d49bde0.  On the next call of
ngx_readv_chain() on systems with EPOLLRDHUP this resulted in return without
any actions, that is, with rev->ready set, and this in turn resulted in no
timers set in event pipe, leading to socket leaks.

Fix is to reset rev->ready in ngx_readv_chain() when returning due to
rev->available being 0 with EPOLLRDHUP, much like it is already done in
ngx_unix_recv().  This ensures that if rev->available will become 0, on
systems with EPOLLRDHUP support appropriate EPOLLRDHUP-specific handling
will happen on the next ngx_readv_chain() call.

While here, also synced ngx_readv_chain() to match ngx_unix_recv() and
reset rev->ready when returning due to rev->available being 0 with kqueue.
This is mostly cosmetic change, as rev->ready is anyway reset when
rev->available is set to 0.

Some servers might emit Content-Range header on 200 responses, and this
does not seem to contradict RFC 9110: as per RFC 9110, the Content-Range
header has no meaning for status codes other than 206 and 416.  Previously
this resulted in duplicate Content-Range headers in nginx responses handled
by the range filter.  Fix is to clear pre-existing headers.

This change partially reverts 2a77754cd9fe to properly free rn->query.

Found by Coverity (CID 1507244).

When set to "off", only IPv6 addresses will be resolved, and no
A queries are ever sent (ticket #2196).

Starting with OpenSSL 1.1.1, various additional errors can be reported
by OpenSSL in case of client-related issues, most notably during TLSv1.3
handshakes.  In particular, SSL_R_BAD_KEY_SHARE ("bad key share"),
SSL_R_BAD_EXTENSION ("bad extension"), SSL_R_BAD_CIPHER ("bad cipher"),
SSL_R_BAD_ECPOINT ("bad ecpoint").  These are now logged at the "info"
level.

To ensure optimal use of memory, SSL contexts for proxying are now
inherited from previous levels as long as relevant proxy_ssl_* directives
are not redefined.

Further, when no proxy_ssl_* directives are redefined in a server block,
we now preserve plcf->upstream.ssl in the "http" section configuration
to inherit it to all servers.

Similar changes made in uwsgi, grpc, and stream proxy.