MSIM: Default NW mode property for each slot

Pick slot specific default Network mode value while
setting Network Mode for new subscription info record.

Bug: 28384694, 36850854
Test: manual - Checked different default NW mode can be set
for each slot.
Test: auto - Confirmed that run SubscriptionInfoUpdaterTest
and PhoneFactoryTest it has no problem.
Change-Id: I72b11522cb51a425e28ddc407014387a20cb2cd7