BUG/MINOR: session: Fix tcp-request session failure if handshake.

BUG/MINOR: session: Fix tcp-request session failure if handshake.

Some sample fetches check if session is established using
the flag CO_FL_CONNECTED. But in some cases, when a handshake
is performed this flag is set too late, after the process
of the tcp-request session rules.

This fix move the raising of the flag at the beginning of the
conn_complete_session function which processes the tcp-request
session rules.

This fix must be backported to 1.8 (and perhaps 1.7)