1. Support identifier in L2TP/IPSec PSK.
2. Fix profile validation for IPSec Hybrid RSA.
3. Fix crash when the user does not want to initialize keystore.
Change-Id: Id46dbbc84915dfb69f8bab6b540426e7614ab7c6
Now users can manually override DNS search domains, DNS servers,
and forwarding routes for each VPN network.
Change-Id: I10b8e383ac19fd19d23938dff78201a71724d58f