VCN: Handle sequence number leap in packet loss detector

This pacth enables IPsec packet loss detector to handle the case when
there is an intentional sequence number leap on the server's downlink.

Previously the detector assumes that sequence number will always
increase consecutively, which is not true. During load balancing the
server might add a big leap on the sequence number intentionally. In
such case a high packet loss rate does not always indicate a lossy
network. At the same time, a low loss rate does mean the network is
not lossy

Bug: 332598276
Test: atest FrameworksVcnTests (new tests) && atest CtsVcnTestCases
Change-Id: I163cb274d293a305499fd60f7ad6eed394af5a4d

Vcn/flags/flags.aconfig

@@ -34,4 +34,14 @@ flag{
     namespace: "vcn"
     description: "Re-evaluate IPsec packet loss on LinkProperties or NetworkCapabilities change"
     bug: "323238888"
+}
+
+flag{
+    name: "handle_seq_num_leap"
+    namespace: "vcn"
+    description: "Do not report bad network when there is a suspected sequence number leap"
+    bug: "332598276"
+    metadata {
+      purpose: PURPOSE_BUGFIX
+    }
 }