smpp: don't enqueue write messages if ESME is disconnected

If the ESME has been disconnected (dead socket) but still is
in memory (other users hold a use count), we shouldn't enqueue
messages to the write queue.

This prevents messages like
DSMPP write_queue.c:112 wqueue(0x7f8bc392f6e0) is full. Rejecting msgb

Change-Id: I10a270f1d555782be272f4d78da43190618a9950
Closes: OS#3278
1 file changed