net: use socket_set_nodelay() for -netdev socket

net: use socket_set_nodelay() for -netdev socket

Reduce -netdev socket latency by disabling the Nagle algorithm on
SOCK_STREAM sockets in net/socket.c.  Since we are tunelling Ethernet
over TCP we shouldn't artificially delay outgoing packets, let the guest
decide packet scheduling.

I already get sub-millisecond -netdev socket ping times on localhost, so
there was no measurable difference in my testing.  This won't hurt
though and may improve remote socket performance.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>