osmo_io_poll: Handle -EAGAIN in case of OSMO_FD_WRITE

Related: OS#6213
Change-Id: I59c86370d13f2bb33c289d1b177df895726975cb
diff --git a/src/core/osmo_io_poll.c b/src/core/osmo_io_poll.c
index d207047..a9aaea4 100644
--- a/src/core/osmo_io_poll.c
+++ b/src/core/osmo_io_poll.c
@@ -86,6 +86,10 @@
 				iofd_txqueue_enqueue_front(iofd, msghdr);
 				return;
 			}
+			if (rc == -EAGAIN) {
+				iofd_txqueue_enqueue_front(iofd, msghdr);
+				return;
+			}
 
 			switch (iofd->mode) {
 			case OSMO_IO_FD_MODE_READ_WRITE: