MYNEWT-698: Unhandled exception in controller in ble_ll_conn_end
MYNEWT-698: Unhandled exception in controller in ble_ll_conn_end

The controller was generating an unhandled exception inside the
function ble_ll_conn_end. This was occurring when the controller
was scheduling a new connection (master role) but no mbufs were
available to hand the received pdu to the link layer task. The
code attempts to schedule a master role connection and send a
connection request prior to allocating a receive buffer for the
received advertising pdu. It does this to save time since we need
all the time available from when the advertising pdu is received
until the time we need to send the connect request.

I am not terribly pleased with the fix since it is inefficient.
However, I wanted to get a fix in now. A better way might not be
to re-enable scanning or initiating unless a buffer is available
for receive but that change would be a bit more work.

andrzej-kaczmarek/incubator-mynewt-core,mlaz/mynewt-core,wes3/incubator-mynewt-core,wes3/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,IMGJulian/incubator-mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/apache-mynewt-core,IMGJulian/incubator-mynewt-core,wes3/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,IMGJulian/incubator-mynewt-core,wes3/incubator-mynewt-core,IMGJulian/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,wes3/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,mlaz/mynewt-core,IMGJulian/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core