all: make copyright headers consistent with one space after period

Go policy has been single space after periods in comments for some time.

The copyright header template at:

	https://golang.org/doc/contribute.html#copyright

also uses a single space.

Make them all consistent.

This CL was generated with:

	perl -i -npe 's,^(// Copyright [0-9]+ The Go Authors\.)  (All rights reserved\.)$,$1 $2,' $(git grep -l -E '^// Copyright [0-9]+ The Go Authors\.  All rights reserved\.$')

Follows https://golang.org/cl/20111.

Change-Id: I66671dddf821f5dc027bc254e0196b3e3a2bdf3b
Reviewed-on: https://go-review.googlesource.com/32878
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/ipv4/genericopt_posix.go b/ipv4/genericopt_posix.go
index f333581..58168b7 100644
--- a/ipv4/genericopt_posix.go
+++ b/ipv4/genericopt_posix.go
@@ -1,4 +1,4 @@
-// Copyright 2012 The Go Authors.  All rights reserved.
+// Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.