netmap: Make memory pools NUMA-aware

Each netmap adapter associated with a physical adapter is attached to a
netmap memory pool. contigmalloc() is used to allocate physically
contiguous memory for the pool, but ideally we would ensure that all
such memory is allocated from the NUMA domain local to the adapter.

Augment netmap's memory pools with a NUMA domain ID, similar to how
IOMMU groups are handled in the Linux port. That is, when attaching to
a physical adapter, ensure that the associated memory pools are local to
the adapter's associated memory domain, creating new pools as needed.

Some types of ifnets do not have any defined NUMA affinity; in this case
the domain ID in question is the sentinel value -1.

Add a sysctl, dev.netmap.port_numa_affinity, which can be used to enable
the new behaviour. Keep it disabled by now to avoid surprises in case
netmap applications are relying on zero-copy optimizations to forward
packets between ports belonging to different NUMA domains.

Reviewed by: vmaffione
MFC after: 2 weeks
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D46666