Comparison of unsigned expression < 0 is always false

When compiling the latest master, clang points out that some of your comparisons are tautological:

vxlan.c:108:10: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
        if (len < 0)
            ~~~ ^ ~

vde_autolink.c:865:41: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
        if( (curlink->portno = port_reserve()) < 0 ){
            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~

wirefilter.c:214:12: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                if (next < 0) next=0;
                    ~~~~ ^ ~

wirefilter.c:1638:35: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                                (markovdelay < delay || delay < 0)) delay=markovdelay;
                                                        ~~~~~ ^ ~

wirefilter.c:1649:38: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                                        if (speeddelay < delay || delay < 0) delay=speeddelay;
                                                                  ~~~~~ ^ ~

wirefilter.c:1664:39: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                                                if (speeddelay < delay || delay < 0) delay=speeddelay;
                                                                          ~~~~~ ^ ~

Start at the warning sites in vxlan.c:108, vde_autolink.c:865, and wirefilter.c:214, 1638, 1649, and 1664, then inspect the declared types and surrounding logic. Compile with clang to reproduce the warnings; done means the listed tautological-comparison warnings are resolved without changing intended behavior.