Check for combined channel bandwidths for LTE+ icon

Most carriers only show the LTE+ icon if the combined channel bandwidth
is greater than 20 MHz. In NetworkTypeController, check that the
combined bandwidth meets the carrier config requirements before
displaying the LTE+ icon.

Test: atest NetworkTypeController
Bug: 160873305
Change-Id: I6b536007ef1aaed270cfd2aeedbffa58ec01b966