BUG/MEDIUM: streams: Remove SF_ADDR_SET if we're retrying due to L7 retry.

BUG/MEDIUM: streams: Remove SF_ADDR_SET if we're retrying due to L7 retry.

In do_l7_retry(), remove the SF_ADDR_SET flag. Otherwise,
assign_server_address() won't be called again, which means for 2.1 or 2.2,
we will always retry to connect to the server that just failed, and for 2.0,
that we will try to use to whatever the address is for the connection,
probably the last server used by that connection before it was pool_free()
and reallocated.

This should be backported to 2.1 and 2.0.