Add macro for BPF_HASH about bcc HOT 3 CLOSED

Or even supporting both explicit or implicit value types (3rd argument optional):

BPF_HASH(start, struct request *, u64);
BPF_HASH(start, struct request *);

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This has been working, so the ticket can be closed.

It works for hashes that exist only for the C program; eg, temporarily storing timestamps.

I hit issues accessing a BPF_HASH() key (when a key_t is not in use, like in the example above) from Python, complaining about it not being c_int, but that can be a separate issue.

from bcc.

For the python case you mentioned, what I tend to do is wrap things that should be a ctype with a Table.Key() or Table.Leaf() type.

For instance, if Key is a complex type like struct { int a; int b; }:

b["stats"][b["stats"].Key(0, 1)] = b["stats"].Leaf(42)

from bcc.