switch AF_PACKET and AF_UNIX to skb_copy_datagram_from_iter()

... and kill skb_copy_datagram_iovec()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc include/linux/skbuff.h
Simple merge

diff --cc net/core/datagram.c
Simple merge

diff --cc net/packet/af_packet.c
Simple merge

diff --cc net/unix/af_unix.c
Simple merge