Patch for gr-osmosdr

Hi I have a patch for the gr-osmosdr project that I am hoping you will be able to merge into the repo. The patch makes it possible to choose which hackrf is opened by the sink component. It also moves the hackrf_open code into a separate, shared source file that is used by both the sink and the source components. Initially I tried to do a Pull Request on the Github repository, but was told I should send a patch to this mailing list. What format should I use to send the patch? Regards Mike Davis