6.1.0 sitl interop (#8913)
* fix getopts 'has_arg' usage (iaw getopt_long(3))
* Rexec the SITL on reboot
* Allow hostnames, facilitate compilation on non-GNU OS (e.g. *BSD), add IPV6 [xplane.c]
* add required interop header files [simple_soap_client.c]
* add required interop header files [simple_soap_client.h]
* update serial_tcp (headers, IPv6, lookup etc)
* conditional for pthread_attr_getschedpolicy availability
* fix error in xplane socket familiy
* remove unnecessary added headers [xplane.c]
* fix gcc 12 warning is osd.c
* update docs
* fix for older gcc without closefrom(3)
* add AI_V4MAPPED|AI_ADDRCONFIG to ai_flags (to support V4 only hosts)