Kernel prepatch 7.3-rc1

Linus has released 7.3-rc1 and closed the merge window for this release. "Nothing really stands out - except for the fact that it's big. It's not the biggest rc1 we've ever had, but it's certainly up there, at least in number of commits." He pulled 15,267 commits during this merge window, making it the second busiest ever; only 6.7 has exceeded it.