net: add .gitattributes (fixes windows build)

Fixes #9281

Change-Id: I144afc9736d3d0ba1cdd2693efd0c7f07b1b8bf3

.gitattributes

+# Treat all files in this repo as binary, with no git magic updating
+# line endings. Windows users contributing to Go will need to use a
+# modern version of git and editors capable of LF line endings.
+#
+# We'll prevent accidental CRLF line endings from entering the repo
+# via the git-review gofmt checks.
+#
+# See golang.org/issue/9281
+
+* -text