Make DEFAULT_PREFERRED_NETWORK_MODE @hide for now

This API also needs to expose the possible values which would need more
work hence we will drop this for now and re-work for next release

This CL also fixes a bug to use correct RIL constant

Bug: 148514283
Bug: 148484234
Test: Verified that the eSIM works on DSDS
      atest packages/services/Telephony/tests/
      atest frameworks/opt/telephony/tests/telephonytests/

Change-Id: Ifd7b17cc2445c9cbe4c6ba688838a1b07eb13599