IPSec: Set default unique ID behavior

Prevent an incoming connection request from our peer from
disrupting an ongoing connection.  The default behavior is for
such a connection to replace any ongoing SAs.

BUG=chromium:372038
TEST=Unit tests + network_VPNConnect.l2tpipsec_psk for regression
and manual: connect to Cisco VPN that originally highlighted this
issue.

Change-Id: Ifde31b5988588f894e18a65b2bc8f45c26afb6fe
Reviewed-on: https://chromium-review.googlesource.com/203646
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
diff --git a/ipsec_manager.cc b/ipsec_manager.cc
index c5a25e9..e5b62ff 100644
--- a/ipsec_manager.cc
+++ b/ipsec_manager.cc
@@ -367,6 +367,7 @@
   if (debug()) {
     AppendStringSetting(&config, "charondebug", "dmn 2, mgr 2, ike 2, net 2");
   }
+  AppendStringSetting(&config, "uniqueids", "no");
 
   config.append("conn managed\n");
   AppendStringSetting(&config, "ike", FLAGS_ike);
diff --git a/ipsec_manager_test.cc b/ipsec_manager_test.cc
index 79811de..8b1c93f 100644
--- a/ipsec_manager_test.cc
+++ b/ipsec_manager_test.cc
@@ -340,6 +340,7 @@
   if (debug) {
     expected.append("\tcharondebug=\"dmn 2, mgr 2, ike 2, net 2\"\n");
   }
+  expected.append("\tuniqueids=\"no\"\n");
   expected.append(
       "conn managed\n"
       "\tike=\"3des-sha1-modp1024\"\n"
@@ -422,6 +423,7 @@
   if (debug) {
     expected.append("\tcharondebug=\"dmn 2, mgr 2, ike 2, net 2\"\n");
   }
+  expected.append("\tuniqueids=\"no\"\n");
   expected.append(
       "conn managed\n"
       "\tike=\"3des-sha1-modp1024\"\n"