Add an explicit hash_delete() function.
Cache node IDs in a hash table for faster lookups.
Avoid memmove() for legacy UDP packets.
Make UDP packet handling more efficient.

Limit the amount of address/ID lookups to the minimum in all cases:

1) Legacy packets, need an address lookup.
2) Indirect SPTPS packets, need an address lookup + two ID lookups.
3) Direct SPTPS packets, need an ID or an address lookup.

So we start with an address lookup. If the source is an 1.1 node, we know it's an SPTPS packet,
and then the check for direct packets is a simple check if dstid is zero. If not, do the srcid and dstid
lookup. If the source is an 1.0 node, we don't have to do anything else.

If the address is unknown, we first check whether it's from a 1.1 node by assuming it has a valid srcid
and verifying the packet. If not, use the old try_harder().