MEDIUM: stconn: take SE_FL_APPLET_NEED_CONN out of the RXBLK_ANY flags

MEDIUM: stconn: take SE_FL_APPLET_NEED_CONN out of the RXBLK_ANY flags

This makes SE_FL_APPLET_NEED_CONN autonomous, in that we check for it
everywhere we have a relevant cs_rx_blocked(), so that the flag doesn't
need anymore to be covered by cs_rx_blocked(). Indeed, this flag doesn't
really translate a receive blocking condition but rather a refusal to
wake up an applet that is waiting for a connection to finish to setup.

This also ensures we will not risk to set it back on a new endpoint
after cs_reset_endp() via SE_FL_APP_MASK, because the flag being
specific to the endpoint only and not to the connector, we don't
want to preserve it when replacing the endpoint.

It's possible that cs_chk_rcv() could later be further simplified if
we can demonstrate that the two tests in it can be merged.