allow custom paths for chaining
allow custom paths for chaining

by moving from current_hop to pathindex we can allow loops in the path.

One problem still remains: paths containing a loop with a single hop will not be set up correctly.
say: s1 -> s2 -> s1
as the 'IN_PORT' command is needed, that ryu does not support.
knodir/son-emu,knodir/son-emu,knodir/son-emu,knodir/son-emu