Cannot combine -l and expressions

[Bklyn]

Using -l means you cannot also provide a filter expression to tcpflow. I'd propose the following possible solutions:

• Allow use of "response files" with -r, signalling them with a leading @ (i.e. tcpflow -r @file-with-filenames). This gets around the need to pass overly-long command lines
• Add another command line argument (!) for specifying the expression string

I'd personally prefer the first option and will submit a PR for it.