Add Knot interface as another input format

Add support for new interface presented in Knot 3.0.6 as another input format. This interface uses unix sockets to transport Knot defined datagrams which contain already paired queries and responses so pairing in transaction table can be skipped in the probe.

New options in configuration file and command line arguments are added: knot-socket-count (-k) and knot-socket-path (-s).