misc: Add util/packet_pb2.py to .gitignore.

This file is automatically generated and not managed by git.

Change-Id: I077fe1ad89b65716a829b783a8b9c6e23b4d0b6b
Reviewed-on: https://gem5-review.googlesource.com/5006
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
diff --git a/.gitignore b/.gitignore
index 6f849bf..6075ffe 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,6 +14,7 @@
 /util/m5/*.o
 /util/m5/*.a
 /util/m5/m5
+/util/packet_pb2.py
 /util/tap/*.d
 /util/tap/*.o
 /util/tap/m5tap