Including changes to mnexec -c to reduce the number of
close() system calls, which may help with performance in
containers on Ubuntu 22.04.
Note that systemd-udevd also seems to be a cause of performance issues
and should probably be disabled while running Mininet.
Adding dbeug logging to test_simpleperf because it is failing
intermittently. (Note with packet loss it can fail, but this
is not how we should be testing it.)
lantz
88f14e946a