[LES] Servers should peer with servers if they have no peers

[immesys]

System information

Geth version: 1.5.9
OS & Version: Linux
Commit hash : my own hacked fork, but changes likely not relevant

Expected behaviour

A private network consisting of nodes having --lightserv 50 --lightpeers 20 in the absence of light clients will function the same as without those flags

Actual behaviour

Light servers will refuse to peer with light servers leading to peer starvation in the case that all nodes are light servers. E.g:

DEBUG[04-07|03:12:34] Light Ethereum handshake failed          id=4bb411a7c77b12c5 conn=inbound err=" - wanted client, got server"
TRACE[04-07|03:12:34] Protocol les/1 failed                    id=4bb411a7c77b12c5 conn=inbound err=" - wanted client, got server"
DEBUG[04-07|03:12:34] Ethereum message handling failed         id=4bb411a7c77b12c5 conn=inbound err=EOF
DEBUG[04-07|03:12:34] Removing Ethereum peer                   peer=4bb411a7c77b12c5
TRACE[04-07|03:12:34] Unregistering sync peer                  peer=4bb411a7c77b12c5

which basically leads to all nodes having no peers at all.

Steps to reproduce the behaviour

Try running a few geth nodes where all reachable peers are light servers (either private network or net restrict)

[immesys]

Thanks!

[karalabe]

@immesys Could you verify that it works for you now? Just want to make sure before releasing it.

[immesys]

Sure, I can test this