net: replace error variable name e, errno with err

R=rsc, r
CC=golang-dev
https://golang.org/cl/5593046
diff --git a/src/pkg/net/sendfile_linux.go b/src/pkg/net/sendfile_linux.go
index e9ab066..7f51519 100644
--- a/src/pkg/net/sendfile_linux.go
+++ b/src/pkg/net/sendfile_linux.go
@@ -48,23 +48,23 @@
 		if int64(n) > remain {
 			n = int(remain)
 		}
-		n, errno := syscall.Sendfile(dst, src, nil, n)
+		n, err1 := syscall.Sendfile(dst, src, nil, n)
 		if n > 0 {
 			written += int64(n)
 			remain -= int64(n)
 		}
-		if n == 0 && errno == nil {
+		if n == 0 && err1 == nil {
 			break
 		}
-		if errno == syscall.EAGAIN && c.wdeadline >= 0 {
+		if err1 == syscall.EAGAIN && c.wdeadline >= 0 {
 			pollserver.WaitWrite(c)
 			continue
 		}
-		if errno != nil {
+		if err1 != nil {
 			// This includes syscall.ENOSYS (no kernel
 			// support) and syscall.EINVAL (fd types which
 			// don't implement sendfile together)
-			err = &OpError{"sendfile", c.net, c.raddr, errno}
+			err = &OpError{"sendfile", c.net, c.raddr, err1}
 			break
 		}
 	}