Speedup interface lookup

In the interface code (iface_mgr.*) it is noted that the current structure (list) is not efficient for lookups (both by name and by index use a FOREACH). I suggest to switch to a multi index:

• name index should be unordered (hash should be better than RB tree according to the common naming) and unique.
• index should be ordered, unique and be the first index so iterations will use it (based on the assumption interfaces are scanned by increasing index so it should be similar to the current behavior)

Note that C library routines should be never used in place performance matters as they simply rescan the whole interface list...