Update NR TAC limit to 3 bytes

TAC was updated to 3 bytes, so the limit is now 0xffffff instead of the
previous 0xffff. Update to meet 3GPP requirements in 24.501 9.11.3.8.

Test: build
Bug: 144433329
Change-Id: Ie007c29671da709f23684ff27d30ef1c377aadc6