Merge branch 'selftests-updates-to-allow-single-instance-of-nettest-for-client-and-server'

David Ahern says:

====================
selftests: Updates to allow single instance of nettest for client and server

Update nettest to handle namespace change internally to allow a
single instance to run both client and server modes. Device validation
needs to be moved after the namespace change and a few run time
options need to be split to allow values for client and server.

v4
- really fix the memory leak with stdout/stderr buffers

v3
- send proper status in do_server for UDP sockets
- fix memory leak with stdout/stderr buffers
- new patch with separate option for address binding
- new patch to remove unnecessary newline

v2
- fix checkpath warnings
====================

Link: https://lore.kernel.org/r/20210114030949.54425-1-dsahern@kernel.orgSigned-off-by: NJakub Kicinski <kuba@kernel.org>