Merge branch 'Sockmap copying'

Lorenz Bauer says:

====================
Changes in v2:
- Check sk_fullsock in map_update_elem (Martin)

Enable calling map_update_elem on sockmaps from bpf_iter context. This
in turn allows us to copy a sockmap by iterating its elements.

The change itself is tiny, all thanks to the ground work from Martin,
whose series [1] this patch is based on. I updated the tests to do some
copying, and also included two cleanups.

I'm sending this out now rather than when Martin's series has landed
because I hope this can get in before the merge window (potentially)
closes this weekend.

1: https://lore.kernel.org/bpf/20200925000337.3853598-1-kafai@fb.com/
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>