BUG/MINOR: tcpcheck: Set socks4 and send-proxy flags before the connect call

BUG/MINOR: tcpcheck: Set socks4 and send-proxy flags before the connect call

Since the health-check refactoring in the 2.2, the checks through a socks4 proxy
are broken. To fix this bug, CO_FL_SOCKS4 flag must be set on the connection
before calling the connect() callback function because this flags is checked to
use the right destination address. The same is done for the CO_FL_SEND_PROXY
flag for a consistency purpose.

A reg-test has been added to test the "check-via-socks4" directive.

This patch must be backported to 2.2.