Add the description of "-netdev stream" and "-netdev dgram" in the QEMU
manpage.
Add some examples on how to use them, including a way to use
"-netdev stream" and "passt" in place of "-netdev user".
("passt" is a non privileged translation proxy between layer-2,
like "-netdev stream", and layer-4 on host, like TCP, UDP,
ICMP/ICMPv6 echo)
Was there any plan to have passt fallback (default / "-net passt") when slirp is disabled ? spawning the process with -F fd etc. That would help migrating away from slirp for some systems.