When an error happens in the update sockmap element logic also pass
the err up to the user.

Fixes: e5cd3abc ("bpf: sockmap, refactor sockmap routines to work with hashmap")
Signed-off-by: NJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>