Add Functions to flush SADB, Policy DB, and Ifaces

-Add ipSecFlushState() which flushes the kernel's
 SA DB and Policy DB.
-Add ipSecFlushInterfaces() which seeks and removes
 any interfaces that have the prefix 'ipsec'
-Automatically call these functions when netd restarts
-Make XfrmController's methods static
-Add integration tests to verify flushing of policy
 states, and interfaces
-Convert XfrmController functions to static for easier
 test-ability

Bug: 74560705
Test: runtest ...netd_integration_test.cpp
Change-Id: Id60e7c29ff9aeee7f5ccd505b86c94cce858745f