iovec: move memcpy_from/toiovecend to lib/iovec.c

iovec: move memcpy_from/toiovecend to lib/iovec.c

ERROR: "memcpy_fromiovecend" [drivers/vhost/vhost_scsi.ko] undefined!

commit a799d04b18e16c3f33f95f5e78549fa4c7c65017
    vhost-scsi: Include prot_bytes into expected data transfer length
in target-pending makes drivers/vhost/scsi.c call memcpy_fromiovecend().
This function is not available when CONFIG_NET is not enabled.

socket.h already includes uio.h, so no callers need updating.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>