webrtcbin: datachannels critical error in 1.16

It seems the datachannel implementation in 1.16 works only one way, e.g. from python to browser but not the other way around.

Here is a stack trace from 1.16.2:

** (python3:20643): CRITICAL **: 21:14:54.492: _data_channel_have_sample: assertion 'channel->sctp_transport != NULL' failed

Thread 62 "sctpdec1:src_1" received signal SIGTRAP, Trace/breakpoint trap.
[Switching to Thread 0x7f4e7fc1e0 (LWP 20720)]
__GI_raise (sig=<optimized out>) at ../sysdeps/unix/sysv/linux/raise.c:50
50	in ../sysdeps/unix/sysv/linux/raise.c
(gdb) info stack
#0  __GI_raise (sig=<optimized out>) at ../sysdeps/unix/sysv/linux/raise.c:50
#1  0x0000007fb61e0980 in g_logv () at /usr/lib/aarch64-linux-gnu/libglib-2.0.so.0
#2  0x0000007fb61e0b50 in g_log () at /usr/lib/aarch64-linux-gnu/libglib-2.0.so.0
#3  0x0000007fb53befec in _data_channel_have_sample (error=0x7f4e7fb348, sample=0xfccac0, channel=0x7f78018830) at webrtcdatachannel.c:587
#4  on_sink_sample (sink=<optimized out>, user_data=0x7f78018830) at webrtcdatachannel.c:701
#5  0x0000007fb5389f64 in gst_app_sink_render_common (psink=0x7f7801ba00, data=0x7f3c006a20, is_list=<optimized out>) at gstappsink.c:935
#6  0x0000007fb53330ec in  () at /usr/lib/aarch64-linux-gnu/libgstbase-1.0.so.0
#7  0x0000007fb5333e94 in  () at /usr/lib/aarch64-linux-gnu/libgstbase-1.0.so.0
#8  0x0000007fb549a208 in  () at /usr/lib/aarch64-linux-gnu/libgstreamer-1.0.so.0
#9  0x0000007fb549be10 in  () at /usr/lib/aarch64-linux-gnu/libgstreamer-1.0.so.0
#10 0x0000007fb54a3374 in gst_pad_push () at /usr/lib/aarch64-linux-gnu/libgstreamer-1.0.so.0
#11 0x0000007f981c2d38 in gst_sctp_data_srcpad_loop (pad=0x7f780161c0) at gstsctpdec.c:382
#12 0x0000007fb54d56fc in  () at /usr/lib/aarch64-linux-gnu/libgstreamer-1.0.so.0
#13 0x0000007fb62038f8 in  () at /usr/lib/aarch64-linux-gnu/libglib-2.0.so.0
#14 0x0000007fb6202f64 in  () at /usr/lib/aarch64-linux-gnu/libglib-2.0.so.0
#15 0x0000007fb7e0a4fc in start_thread (arg=0x7f9affa59f) at pthread_create.c:477
#16 0x0000007fb7f05f2c in thread_start () at ../sysdeps/unix/sysv/linux/aarch64/clone.S:78
(gdb)

For simple demo, I added gst-examples!19 (closed)