amarisoft/callbox: raise low MTU to 1400

1300 seems to be causing problems with connectivity but 1400 works OK.

BUG=None
TEST=cellular.MTU.low_mtu and cellular.MTU.low_mtu_modb_no_override

Change-Id: Ifafe3aee65c4702ec7f9c2235280712d606aaa93
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/4743770
Reviewed-by: Andrew Lassalle <andrewlassalle@chromium.org>
Tested-by: Eric Caruso <ejcaruso@chromium.org>
Commit-Queue: Eric Caruso <ejcaruso@chromium.org>
diff --git a/src/chromiumos/test/callbox/amarisoft/mme/config/cros_pdn_list_all.cfg b/src/chromiumos/test/callbox/amarisoft/mme/config/cros_pdn_list_all.cfg
index e3c9f5e..19e143c 100644
--- a/src/chromiumos/test/callbox/amarisoft/mme/config/cros_pdn_list_all.cfg
+++ b/src/chromiumos/test/callbox/amarisoft/mme/config/cros_pdn_list_all.cfg
@@ -70,7 +70,7 @@
       access_point_name: "callbox-ipv4-low-mtu",
       first_ip_addr: "192.168.9.2",
       last_ip_addr: "192.168.9.254",
-      mtu_ipv4: 1300,
+      mtu_ipv4: 1400,
       dns_addr: "192.168.9.1",
       include "cros_erabs_var.cfg",
     },