const golang.org/x/sys/unix.IPPROTO_GRE

one use

	golang.org/x/sys/unix (current package)
		zerrors_linux.go#L1552: 	IPPROTO_GRE                                 = 0x2f

The pages are generated with Golds v0.7.6. (GOOS=linux GOARCH=amd64)