Add a .gitignore for packages/modules/NetworkStack.

Test: repo upload
Change-Id: I0b2815bc41787422f8d0b4e5f07a997a68047541
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..2732435
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,7 @@
+# Generated build files
+gen/com/android/networkstack/**
+
+# IntelliJ project files
+**/.idea
+**/*.iml
+**/*.ipr