Use non-extended mockito for net-tests-utils

Mockito extended tends to cause all kinds of issues due to the way it
injects itself into the bytecode of framework classes instead of
creating subclasses.

Use non-extended mockito as it is not actually necessary for current
tests.

Test: atest
Change-Id: Id2874309cce2778c4405b852df9a3ae816c4abcb
4 files changed