Enhancement: provide maximum ETX threshold for routing.

[NickSchmitz]

Is your feature request related to a problem? Please describe.
Many connections are too many hops away to provide any useful bandwidth of connections
to allow listed services to function. Causes excess routing traffic.

Describe the solution you'd like
Provide an On/Off switch & ETX threshold number disable node routing.
Off - current routing behavior - all connections routed regardless of ETX
On - ETX less than threshold (4.0 default) are routed.

Default should be Off to minimize impact to casual user.

Discussed with OrvB on zoom call - 4/22