Panic when two messages arrive at the same time

[Varunram]

When two invalid messages arrive quickly, one after the other before we can connect to a new node, this results in lit trying to connect twice to a node from the DNS Peers. Suppose the list of DNSSeeds is in itself filled with spam nodes, both connections from the previous a attempts fail and each spawns its own two Connections requests and so on. This finally leads to a segfault since there isn't enough memory. Will put in a PR to solve this.

[Varunram]

PR: #323

[Varunram]

Closed via https://github.com/mit-dci/lit/commit/30d3dc84be770257d744898699ac7d3d4eae3962