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 v3 -> v4
Fixed warning introduced in vnc.c

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


Rich: BTW, this should not have any impacts to migration; it only
enables keepalives for VNC and TCP-based char devices.

david