Add SPDX license id and copyright banners to source files needing them#545

jafingerhut wants to merge 3 commits intop4lang:mainp4lang/p4runtime:mainfrom

jafingerhut:add-license-id-and-copyright-banners-to-source-filesjafingerhut/p4runtime:add-license-id-and-copyright-banners-to-source-filesCopy head branch name to clipboard