dhcp: don't reset pid on client exit

Clients in IPv6 info-only mode may exit after getting a response
from the server, since there are no leases involved in info-only
mode.  To ensure that the client's options are received when the
event comes in (which could be after we get the child watch
callback for the exit) we still need the client's PID.

src/dhcp-manager/nm-dhcp-client.c

@@ -227,7 +227,6 @@ daemon_watch_cb (GPid pid, gint status, gpointer user_data)
 		nm_log_warn (LOGD_DHCP, "DHCP client died abnormally");
 	} else
 		priv->state = DHC_END;
-	priv->pid = -1;
 
 	watch_cleanup (self);
 	timeout_cleanup (self);