meta-google: gbmc-bridge: accept all bmc initiated connection

All traffic to/from tray are via gbmcbr. We need to allow the incoming
traffic that establish a tcp connection to allow bmc client traffic like
netboot downloading. This add a rule for that.

Change-Id: I2f3afeea6320b20d7e0f740b102b2f227799032d
Signed-off-by: Yuxiao Zhang <yuxiaozhang@google.com>
diff --git a/meta-google/recipes-google/networking/gbmc-bridge/50-gbmc-br.rules b/meta-google/recipes-google/networking/gbmc-bridge/50-gbmc-br.rules
index 475cc02..9d82e61 100644
--- a/meta-google/recipes-google/networking/gbmc-bridge/50-gbmc-br.rules
+++ b/meta-google/recipes-google/networking/gbmc-bridge/50-gbmc-br.rules
@@ -12,6 +12,7 @@
   chain gbmc_br_input {
     type filter hook input priority 0; policy drop;
     iifname != gbmcbr accept
+    ct state established accept
     jump gbmc_br_int_input
     jump gbmc_br_pub_input
     reject