Propose to merge `netlink-packet-utils` and `netlink-packet-core`

[cathay4t]

There is no clear line between what should be stored in core or utils.

Can we just merge utils into netlink-packet-core to hold the shared functions among all netlink-packet-xxx crates.

[cathay4t]

@little-dude @JohnTitor

[pront]

This is a good idea. The current split can create bad situations: vectordotdev/vector#22811 (comment)