vhost/vsock: support SEQPACKET for transport

When received packet is copied to guests's rx queue, data buffers
of rx queue could be smaller that data buffer of input packet, so
data of input packet is copied to each rx buffer, thus each rx
buffer will be a packet with dynamically created header. Fields
of such header are initialized from header of input packet(except
length field which value is depends on number of bytes copied to
rx buffer). But in SEQPACKET case, we also need to take care of
record delimeter bit: if input packet has this bit set, we don't
copy it to header of packet in rx buffer, except case when such
rx buffer is last part of input packet. Otherwise, we will get
sequence of packets with delimeter bit set, thus braking record
bounds.
Also remove ignore of non-stream type of packets, handle SEQPACKET
feature bit.

Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
Signed-off-by: David S. Miller <davem@davemloft.net>