babeld: fix interface bug, simplify code.

Perhaps could it be able to free already free memory (so free(NULL)),
in function interface_reset().  On other hand, it initiated untracked
interfaces, raising (at least) inappropriate messages. Finally, I
remove the BABEL_IF_IS_ENABLE flag, witch was not really usefull.
Note the test if_up isn't weaker, because (...IS_UP => ...IS_ENABLE).
2 files changed