The net package already has support for limited uses of the strconv
package.  Despite this, a few uses of strconv have crept in over time.
Remove them and use the existing net support instead.

Change-Id: Icdb4bdaa8e1197f1119a96cddcf548ed4a551b74
Reviewed-on: https://go-review.googlesource.com/15400
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>