Ensure that the IPPROTO_TCP level socket options

Ensure that the IPPROTO_TCP level socket options
* TCP_KEEPINIT
* TCP_KEEPINTVL
* TCP_KEEPIDLE
* TCP_KEEPCNT
always always report the values currently used when getsockopt()
is used. This wasn't the case when the sysctl-inherited default
values where used.
Ensure that the IPPROTO_TCP level socket option TCP_INFO has the
TCPI_OPT_ECN flag set in the tcpi_options field when ECN support
has been negotiated successfully.

Reviewed by:	rrs, jtl, hiren
MFC after:	1 month
Differential Revision:	7833