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 b23d6f8)

The '-lrt' added to the Makefile for the common library appears
to be unnecessary.

- On modern Linuxes, this library has been merged with libc, and the
  supplied library is empty.
- On older ones (e.g. Devuan 4), the library contains routines we
  do not use in xrdp (although we use 'shm_open()' in xorgxrdp).
- On FreeBSD 14 the library contains only mq_*  and timer_* routines
  which, again, are not required.

(cherry picked from commit e821edd)

This script now works the same way as cppcheck. The version to
be used is specified once in the github CI action

(cherry picked from commit b9fd19e)

(cherry picked from commit 651fcf8)

The user socket directory needs to be SGID so that they inherit
the group ownnership. Then xrdp can write to them.

(cherry picked from commit 200e4d8)

- The command 'systemd-analyze syscall-filter' shows that the group
  @System-service added to the xrdp-service SystemCallFilter
  actually includes all of the other listed groups and individual
  services.  Consequently this line can be simplified to just specify
  @System-service.

- (reversion) The SystemCallErrorNumber setting in xrdp.service has been
  removed so that unauthorized system calls cause an immediate process exit.

(cherry picked from commit e0e9177)

…rger than max_compressed_bytes

(cherry picked from commit 95bfb34)

(cherry picked from commit 898e1ca)