configure: fix libnetfilter_conntrack dependency removal

tools_remove "libnetfilter-conntrack" makes no sense, so replace it
with the actual correct tools_remove "flowtop".

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
configure: do not use bash's expr match

It looks like there are some incompatibilities in bash's expr match
among different versions. Using set -x, gives us on bash 4.2.45:

+ TOOLS=' netsniff-ng trafgen ifpps bpfc'
+ for tool in '$_tools'
+ case "$tool" in
++ expr match '"curvetun' 'astraceroute"' '$1'
expr: syntax error
+ m=
+ '[' '' == 0 ']'

So rather avoid using "expr match" and switch to "case" for substring
matching, which should be more portable.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
configure: redirect all compile output to our local config.log

On errors in the configuration, redirect everything to config.log,
and not some parts to config.log and some others to $TMPDIR/config.log.

This will give a nice summary of what goes wrong to the user. Also,
in case everything looks fine, the config.log file will be created,
but with size 0 and no warning is thrown. So looks good.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
configure: fix wrong whitespacing

Not sure how this came in with the last commit, but fix it to the
correct format.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
bpf_comp: pass NEED_TCPDUMP_LIKE_FILTER through gcc

We have to pass NEED_TCPDUMP_LIKE_FILTER define through gcc as it
otherwise is not possible to let the pcap compiler invoke through
netsniff-ng, but not through astraceroute.

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