Fixed that tethering not working

Fixed tethering not working when both DUN and Default
APN type are specified in the APN database. The data connection
with same APN for DUN was brought up incorrectly. We should reuse
the existing default connection for DUN.

Bug: 71562600
Test: Manual tests
Change-Id: Idf52c00d5371aaaa3091c9728a99905ab3b2f471