Alos moves TestTCPSelfConnect into tcpsock_test.go

Change-Id: I3e1cbd029594ecb36a67f42bc3ecdbc7176a95dc
Reviewed-on: https://go-review.googlesource.com/21447
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>