To reduce the bpf.MapKey and bpf.MapValue interface footprints, wind down usage
of DeepCopy methods outside of package bpf. A future commit will replace this
method with New(), which is currently what it's primarily abused for (in
DumpWithCallback and friends).

Map keys and values cannot contain pointer types, so the presence of deep copy
methods is questionable. Copying these types by value should be sufficient to
achieve 'deep' copying behaviour.

The changes in this patch aim to be no-ops:
- The ToHost() methods implemented on lbmap.BackendValue, AffinityMatchKey and
  ServiceValue all copy their receivers by value and already return new copies.
- The callback in policymap dereferences the pointer (and DumpCallbacks already
  receive pointers to unshared copies), so an additional copy is unnecessary.
- The lxcmap callback was changed to dereference the pointers received in the
  callback and return a map of EndpointInfos instead of pointers.

Signed-off-by: Timo Beckers <timo@isovalent.com>