man: ifpps: add bugs section

Add a section of known bugs/todos for bpfc.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
trafgen: do not care if device is running yet

E.g. when executing trafgen on tap devices, trafgen will complain
that it is not up and running although it was brought up. Remove
this usability restriction and let the kernel decide if it may
send the packets or not.

Reported-by: Aimal Khan <aimal.khan98@gmail.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>