nbd-server: split handle_connection()
nbd-server: handle_modern_connection() negotiates
nbd-server: close socket where it was opened
nbd-server: const'd local variables
nbd-server: fix serve pointer in handle_modern_connection()
nbd-server: extract socket accepting
Fix yet another variabe bug
nbd-server: handle_modern_connection also accepts connections
nbd-server: handle_oldstyle_connections also accepts connections