go.net/ipv4: make supportsNewIPInput const
R=dave
CC=golang-dev
https://golang.org/cl/6822083
diff --git a/ipv4/header.go b/ipv4/header.go
index ab17da7..09581bb 100644
--- a/ipv4/header.go
+++ b/ipv4/header.go
@@ -120,7 +120,7 @@
// Please refer to the online manual; IP(4) on Darwin, FreeBSD and
// OpenBSD. IP(7) on Linux.
-var supportsNewIPInput = runtime.GOOS == "linux" || runtime.GOOS == "openbsd"
+const supportsNewIPInput = runtime.GOOS == "linux" || runtime.GOOS == "openbsd"
// Marshal returns the binary encoding of the IPv4 header h.
func (h *Header) Marshal() ([]byte, error) {
