eclass-overlay/profiles: add wpan into group tun

This CL adds wpan to group tun to allow Thread daemon(wpantund) creating
tun device.

CQ-DEPEND=CL:1535920
BUG=b:121291782
TEST=run test_image locally

Change-Id: Ifda68620771c00aa2044d732d21b6ddbbb648a07
Reviewed-on: https://chromium-review.googlesource.com/1525609
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Yakun Xu <xyk@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/profiles/base/accounts/group/tun b/profiles/base/accounts/group/tun
index 871d56f..8d97b6c 100644
--- a/profiles/base/accounts/group/tun
+++ b/profiles/base/accounts/group/tun
@@ -1,4 +1,4 @@
 # Members of this group have write access to /dev/net/tun.
 group:tun
 gid:413
-users:crosvm,shill
+users:crosvm,shill,wpan