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