BUILD: htx: fix fprintf format inconsistency on 32-bit platforms

BUILD: htx: fix fprintf format inconsistency on 32-bit platforms

Building on 32 bits gives this :

  include/proto/htx.h: In function 'htx_dump':
  include/proto/htx.h:443:25: warning: format '%lu' expects argument of type 'long unsigned int', but argument 8 has type 'uint64_t {aka long long unsigned int}' [-Wformat=]
         fprintf(stderr, "htx:%p [ size=%u - data=%u - used=%u - wrap=%s - extra=%lu]\n",
                         ^
In htx_dump(), fprintf() uses %lu but the value is an uint64_t so it
doesn't match on 32-bit. Let's cast this to unsigned long long and use
%llu instead.