This patch enables TCP keepalives on VNC connections and TCP-based char
devices.

Default parameters have keep alive probes sent after 60-seconds of idle
time. Probes are sent every 12 seconds with the connection resetting
after 5 failed probes (ie., connection is closed if no response received
in 60-seconds).

Changes v1 -> v2:
- Added probes to configure
- Moved setsockopt calls into a generic handler named
enable_tcp_keepalive in net.c
- Added call to enable_tcp_keepalive() to vnc and qemu-char

Signed-off-by: David Ahern <dsahern@gmail.com>


david