net: lookup protocol in lower-case on Plan 9
net: lookup protocol in lower-case on Plan 9

Protocol keywords are case-insensitive,
but the Ndb database is case-sensitive.

Also use the generic net protocol instead
of tcp in lookupHost.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/40600047

Committer: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

wesolows/golang,wesolows/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang-old