Do not depend on all of NetworkStack in CTS

Only depend on a newly created DhcpPacketLib library, which only
contains DhcpPacket classes for test usage purposes.

This avoids including the NetworkStack manifest, and many unnecessary
classes.

Test: atest CtsNetTestCases
Change-Id: I0047826ef8bb56f229b296f0b3c337b2de1fbc93
4 files changed