v31 -- hostname changes follow through

Kernel image and binaries unchanged; scripts only.

A hostname change in the web GUI runs 'gl_mdns system restart', which brings the vendor mDNS instance back with its AFP default and leaves every other name stale. The watcher in S99smb now polls the hostname and restarts S99smb and S99discovery on a change, so the SMB server name, WSD, LLMNR, index.html, SSDP and the mDNS registration follow. It also repairs the vendor instance whenever it reappears without -t.

Two related fixes: bonjour() retires every unfixed vendor instance rather than the first (the firmware restarts its own while ours is still up), and stop() no longer starts a second one when the firmware has already done so.

install-smb.sh leaves /root/README-smb.txt on the device: share, accounts, how to change the admin password.

Known issue, fixed in v32: the v23..v31 kernel was built without CONFIG_IP_MULTICAST, so it never sends IGMP reports. Behind a switch with IGMP snooping, SSDP and WSD (239.255.255.250) stop being delivered once the switch's table forgets the port; mDNS and LLMNR (224.0.0.0/24, always flooded) are unaffected.