Fixes polling thread looping forever hangs preventing new connections.
Don't lose listening sockets on mp resets and re-init.
Keep better separation of "system" and "user" sockets.
Track socket states to prevent re-use of sockets before closed.
Close REST socket when transaction completes. No post-init.
Remove unnecessary state flags.
This is the lwip no-os version of SO_REUSEADDR, which is set on all
listening sockets in the espressif port; do so here as well,
it makes running servers easier. The "address in use" error does
not occur.