selftests: lib: forwarding: allow tests to not require mz and jq

These programs are useful, but not all selftests require them.

Additionally, on embedded boards without package management (things like
buildroot), installing mausezahn or jq is not always as trivial as
downloading a package from the web.

So it is actually a bit annoying to require programs that are not used.
Introduce options that can be set by scripts to not enforce these
dependencies. For compatibility, default to "yes".

Cc: Nikolay Aleksandrov <nikolay@nvidia.com>
Cc: Ido Schimmel <idosch@nvidia.com>
Cc: Guillaume Nault <gnault@redhat.com>
Cc: Po-Hsu Lin <po-hsu.lin@canonical.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>