Fixed consistent issue for subId in dataConnection

Currently we get the NetworkCapabilities' specifier from
Phone.getSubId(). This could be different than the one we set when
created the data connection. We should only set the subId when bring up
the data connection.

Bug: 116476933
Test: build
Change-Id: Ie25ee7a7e7227de3c57a297cd0e8367c85bcccba