vpn: Only use AES GCM for Phase 2 Per [1] this does not seem to be supported in IKEv1 Phase 1. Specifying it causes strongSwan to quietly send a malformed proposal, which breaks interop with older clients. [1] https://wiki.strongswan.org/projects/1/wiki/CipherSuiteExamples BUG=chromium:707139 TEST=manually connect to Sophos VPN Change-Id: I6a7dff956659cccab53ca8a78f43852fbdfe8e4b Reviewed-on: https://chromium-review.googlesource.com/487738 Commit-Ready: Kevin Cernekee <[email protected]> Tested-by: Kevin Cernekee <[email protected]> Reviewed-by: Mattias Nissler <[email protected]> Reviewed-by: Maksim Ivanov <[email protected]> (cherry picked from commit c48ff6b7ff70a14e3538d7742ab25401ebcc5935) Reviewed-on: https://chromium-review.googlesource.com/490691 Reviewed-by: Kevin Cernekee <[email protected]> Commit-Queue: Kevin Cernekee <[email protected]>