session: track rx ready state as flag

session: track rx ready state as flag

Instead of checking session state to decide if session layer should
deliver rx notifications to app, on state transition, update rx ready
flag.

This should then avoid generating spurious rx notifications 1) after
session is disconnected by transport and 2) if session is closed prior
to accept with pending rx notification (which 1fce82e allows).

Type: improvement

Change-Id: I2ddd8ae5fe410fdfe4049d09c68cd1fd4dc79b8b
Signed-off-by: Florin Coras <[email protected]>