build: split CFLAGS_DEF and always add CFLAGS_MIN

Currently, when doing a custom "make CFLAGS=...", we run into a compile
error as several necessary defines are not set. Therefore, use override
to always set those.

Reported-by: Marco Belmonte <mbelmonte@globalmedia.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
trafgen: Remove unused local variable in apply_*() functions.

The variable `i' in apply_counter(), apply_randomizer() and
apply_csum16() is only set once, so use the original parameter
`counter_id' instead. Rename `counter_id' to `id' in order to keep it
short.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>