Remove pointless N < 0 checks

route/tc.c:553:9: warning: comparison of unsigned enum expression < 0 is
always false [-Wtautological-compare]
              if (id < 0 || id > RTNL_TC_STATS_MAX)

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>
travis-ci: run `make check` in travis build

Test programs are only compiled when running `make check`.
Also, fix passing $CFLAGS argument to make.

Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>