On Linux, the TCP send buffer size is increased to 32768 if it is less
that this (which it normally is). This however has the effect of disabling
dynamic buffer sizing, leading to a maximum available bandwidth of
max_bandwidth = 262144 (bits) / round_trip_time (secs)
This is not noticeable on a LAN with an RTT of around 0.5ms, but
very noticeable on a WAN with an RTT of 0.25s.
Comments in the config file and manpage in this area are improved, as
is the logging if the parameters are actually set.
(cherry picked from commit b23d6f89d5)
40b0eaf455