vpn-manager: Use LCP echo to keep session alive

Instead of using the "idle" configuration option to automatically
shut down connections, use the "lcp-echo-interval" and
"lcp-echo-failure" to actively monitor the connection state
instead of shutting down idle connections.

BUG=chromium:371563
TEST=network_VPNConnect.l2tpipsec_xauth

Change-Id: I82060e4b709e5ae017197a502c9782fde18b216e
Reviewed-on: https://chromium-review.googlesource.com/199571
Reviewed-by: Ben Chan <[email protected]>
Commit-Queue: Paul Stewart <[email protected]>
Tested-by: Paul Stewart <[email protected]>
2 files changed