misc: add "maxframe" and "rate" to packet-generator cli.

misc: add "maxframe" and "rate" to packet-generator cli.

Allow for setting the maximum number of generated packets to be included
in the frame passed to next nodes. This is very important for testing
code which may be susceptible to multi-frame vs single-frame bugs (e.g.,
code that is doing re-ordering where packets may be buffered between
frames).

Update:
- remove redundant packet "rate" option.
- reduce n_max_frame to u32 as that's what pulled from the CLI.

Type: feature
Signed-off-by: Christian E. Hopps <chopps@chopps.org>
Change-Id: Ie362bbb110b2cf01d9f65c559bbe9101e17b7fdc
Signed-off-by: Christian Hopps <chopps@labn.net>