The Android built-in IPSec client is only a partially-implemented client and does not support the concept of "Group Authentication" and therefore is not compatible with connecting to an ASA as a VPN concentrator server. Period.
This lack has been a sore spot for a very long time and is a major hindrance for corporate/enterprise adoption of Android phones.
You might want to research for the "vpnc" client but as I understand, it requires a rooted phone.