Changes

stream_cli: Fix discard 1st msg received quick after connect

Even if setting osmo_iofd_notify_connected(), it may happen that a read
call-back is triggered towards the user before this
special write-callback is triggered.
stream_cli was already accounting for that in stream_cli_iofd_read_cb()
state STREAM_CLI_STATE_CONNECTING, but was discarding the msgb instead
of pushing it upwards towards the user through read_cb after
transitioning to STREAM_CLI_STATE_CONNECTED.

As a result, eg when an ipaccess client using stream_cli (BTS, liboamo-abis
e1_line ipaccess driver) connected to an ipaccess server (BSC) and the
server quickly transmitted an IPA ID GET, it would get lost.

Related: libosmocore.git Change-Id Ica20a050b98d117995a5b625b23ab9faa61aabee
Change-Id: I98cd51d4bb87d3572245446648ced44a23a622ef