DEBUG: tools: provide a tree dump function for ebmbtrees as well

DEBUG: tools: provide a tree dump function for ebmbtrees as well

It's convenient for debugging IP trees. However we're not dumping the
full keys, for the sake of simplicity, only the 4 first bytes are dumped
as a u32 hex value. In practice this is sufficient for debugging. As a
reminder since it seems difficult to recover the command each time it's
needed, the output is converted to an image using dot from Graphviz:

    dot -o a.png -Tpng dump.txt