pkt-gen: Allow limiting received packets

Makes pkg-gen quit after having received N packets, the same way it
already supports doing for sent packets.

Reviewed by: vmaffione
Sponsored by: Klara Inc.
MFC after: 4 weeks
Differential Revision: https://reviews.freebsd.org/D30266

(cherry picked from commit 20d684ecc9d7d9128774f2e3c287058868f48bb0)

netmap: pkt-gen: fix compilation issue

Remove stray characters preventing the source code from being
compiled.

Fixes: 20d684ecc9d7 ("pkt-gen: Allow limiting received packets").
Submitted by: ar_semihalf.com
Reviewed by: vmaffione
Differential Revision: https://reviews.freebsd.org/D###

(cherry picked from commit 950cf4a29a8e11962cf4672311f685af590c106e)