ipsec: T7225: iOS18+ always requires ExtendedAuthEnabled to be set

If this is unset, loading the iOS VPN profile will error out on the device
giving:

Profile Installation Failed
configuration is invalid:
Missing identity

My first assumption was an empty string in LocalIdentifier for IKE, but turned
out only adding this flag solved it.

This was made optional in commit e97d86e ("T6617: T6618: vpn ipsec
remote-access: fix profile generators") but got reverted now.