hdl_grabber only allows one Velodyne unit to be used at a time

The hdl_grabber module only allows one velodyne module to be used on a given port. In many environments it is necessary to bring in multiple LiDAR units over a network. Due to the code binding to the UDP port, additional units could not be created despite using the IP filter.

• Operating System and version: Windows 7
• Compiler: Visual Studio 2015 (Visual C++ v14)
• PCL Version: 1.80

EDIT: I have tried to attached my working code to fix this issue; however, github is not allowing it at the moment even though it is a zip file. Will try soon. The code may not be perfectly formatted as I am new to submitting to github projects, but it does work. I bring in and fuse 4 LiDAR units using the code.