Fix file permissions for lib/neutron_plugins/linuxbridge_agent

The permissions changed with commit
40aae6adbfce1bd896d5f7b0e281e798b56d1ca8

TrivialFix

Change-Id: I100cb9589309f9289b4581265a5e4206464ddc0e
diff --git a/lib/neutron_plugins/linuxbridge_agent b/lib/neutron_plugins/linuxbridge_agent
old mode 100755
new mode 100644