ability to not bind client

[jkarneges]

TCPKali seems to always bind when connecting. This can make sense if there are multiple network interfaces, but if there is only one interface then binding actually reduces the number of available connections, at least on Linux.

Connections are limited by the number of unique src/dest pairs. If TCPKali makes lots of connections to two IP addresses with one network interface, it should be able to make 64k * 2 total connections. However, when binding, this is limited to just 64k. This doesn't really make sense to me, since I'm not sure how a bind call would affect the uniqueness of src/dest pairs, but maybe I'm overlooking something.

Anyway, commenting out the bind() call in tcpkali lets me make greater than 64k outbound connections with one network interface. Probably there should be an option to disable the bind, or TCPKali should only bind if there is more than one valid interface for the destination.

[jkarneges]

Submitted PR #64.