undo CL 5687057 / 58bc8aae4abb

Fortunately we have never seen the panic on sockaddrToTCP
in the past year.

««« original CL description
net: panic if sockaddrToTCP returns nil incorrectly
Part of diagnosing the selfConnect bug
TBR=dsymonds

R=golang-dev
CC=golang-dev
http://codereview.appspot.com/5687057
»»»

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7137063
cmd/api: sort features

R=golang-dev, minux.ma, bradfitz
CC=golang-dev
https://codereview.appspot.com/7141062
cmd/5l: reduce the size of Prog and Sym

Prog
* Remove the unused Prog* dlink
* note that align is also unused, but removing it does not help due to alignment issues.

Saves 4 bytes, sizeof(Prog): 84 => 80.

Sym
* Align {u,}char fields on word boundaries

Saves 4 bytes, sizeof(Sym): 136 => 132.

Tested on linux/arm and freebsd/arm.

R=minux.ma, remyoudompheng, rsc
CC=golang-dev
https://codereview.appspot.com/7106050