libmsc: fix memory leak (struct gsm_sms) in gsm340_rx_tpdu()

If a MO SMS gets successfully routed through SMPP, we return early
in gsm340_rx_tpdu() and leak a chunk of type 'struct gsm_sms'.

Change-Id: I8a745d747f06baa7109418ffe600b27b3c0a5228
Fixes: [1] Ic34d398e0a850856e20380ae35e5c2ae5e3c539b
Fixes: OS#5334
1 file changed