Remove automatic IKE version negoiation.

According to the strongSwan 4.5.x documentation, the keyexchange configuration value "ike" is a synonym to "ikev2".

In strongSwan 5.0.0 however, the configuration value "ike" will try to negoiate IKEv2 connections but will accept IKEv1 connections if the remote peer sends an IKEv1 request.
Initial MOBIKE Configuration Support

For IKEv2, there is support for MOBIKE which basically allows IPSec connections to roam from interface to interface. When MOBIKE is used, the IKE negoiation phase uses UDP port 4500 rather than using proto-51.

In strongSwan 4.5.x MOBIKE is automatically enabled for IKEv2 connections. We expose the ability to enable/disable MOBIKE to the user.
Merge pull request #6 from TriJetScud/helium-pull-req

Initial MOBIKE Configuration Support
Merge pull request #4 from TriJetScud/helium

Remove automatic IKE version negoiation.