autotest: Fix network_WiFi_SecChange

Apparently this never worked for RSPro setups because hostapd will
forget about the bridge settings after the first association.

TEST=This is a test that now passes on RSPros.
BUG=None

Change-Id: I7f1239e4684433ecaf2a175250375e1579cacc63
Reviewed-on: https://gerrit.chromium.org/gerrit/61215
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
1 file changed