Add tests to ensure 100% line and branch coverage of previously untested
net_buf_linearize() function.
Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>
Move the network buffer tests to tests/lib/net_buf as their implementation
now lives outside of the networking subsystem.
Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>