Change NR TAC to 16777215

Problem:
CellInfoTest#testCellInfo fail
Root cause:
In verifyCellIdentityNr, NR tac is limited to 65536, but in fact
the TAC could reach 16777215(0xffffff).
Solution:
Change max TAC value to 16777215 in test case.

Bug: 181105073
Test: run cts -m CtsTelephonyTestCases -t android.telephony.cts.CellInfoTest#testCellInfo
Change-Id: Icc2031f6203f42d8c01aea1658245ace97507a93