bpfc: Check return value of system()

Check the return value of system() when invoking CPP in the BPF parser
and bail out in case of an error.

This fixes the following compiler warning:

bpf_parser.y:754:9: warning: ignoring return value of ‘system’, declared with attribute warn_unused_result [-Wunused-result]

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
trafgen: Check return value of system()

Check the return value of system() when invoking CPP in the BPF
parser and bail out in case of an error.

This fixes the following compiler warning:

trafgen_parser.y:598:9: warning: ignoring return value of ‘system’, declared with attribute warn_unused_result [-Wunused-result]

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
trafgen: inherit netsniff-ng's -H -Q options

Also make these options available to trafgen.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>