tools: ynl: move the cli and netlink code around

Move the CLI code out of samples/ and the library part
of it into tools/net/ynl/lib/. This way we can start
sharing some code with the code gen.

Initially I thought that code gen is too C-specific to
share anything but basic stuff like calculating values
for enums can easily be shared.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>