stream: bump default buffer size from 2K to 64K

(Only half of the buffer is actually used in a useful way, see manpage
or commit which added the option.)

Might have some advantages with broken network filesystem drivers.

See: #6802

DOCS/man/options.rst

@@ -4197,7 +4197,7 @@ Cache
     Currently, this is used for ``--cache-on-disk`` only.
 
 ``--stream-buffer-size=<bytesize>``
-    Size of the low level stream byte buffer (default: 4KB). This is used as
+    Size of the low level stream byte buffer (default: 128KB). This is used as
     buffer between demuxer and low level I/O (e.g. sockets). Generally, this
     can be very small, and the main purpose is similar to the internal buffer
     FILE in the C standard library will have.

stream/stream.c

@@ -113,7 +113,7 @@ const struct m_sub_options stream_conf = {
     },
     .size = sizeof(struct stream_opts),
     .defaults = &(const struct stream_opts){
-        .buffer_size = STREAM_MIN_BUFFER_SIZE,
+        .buffer_size = 128 * 1024,
     },
 };