configure: fix multiple issues in build configuration

This patch is a bundle of multiple fixes.

1) Fix compilation of astraceroute when HAVE_LIBPCAP=1:
   astraceroute doesn't need libpcap, so add an additional
   guard/define to bpf.h and bpf_comp.c and netsniff-ng.c.
   Also since we generate a config.h file, we do not need
   to have this additional compile flag anymore.

2) Fix tstamping.{h,c} to use the configure script instead
   of the Makefile. For doing this, also fix the object
   inclusion in netsniff-ng/Makefile.

Last but not least, rename __WITH_... into HAVE_... as this
is more clean.

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