net: netpoll: Individualize the skb pool

The current implementation of the netpoll system uses a global skb
pool, which can lead to inefficient memory usage and
waste when targets are disabled or no longer in use.

This can result in a significant amount of memory being unnecessarily
allocated and retained, potentially causing performance issues and
limiting the availability of resources for other system components.

Modify the netpoll system to assign a skb pool to each target instead of
using a global one.

This approach allows for more fine-grained control over memory
allocation and deallocation, ensuring that resources are only allocated
and retained as needed.

Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20241114-skb_buffers_v2-v3-1-9be9f52a8b69@debian.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>