[sr-dev] [kamailio/kamailio] WebSocket keepalive logging "forcibly closing connection" with TCP connection errors (Issue #2990)

[Max Wardell]

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### Description

Similar to [issue #1886](https://github.com/kamailio/kamailio/issues/1886), we have Kamailio receiving WebRTC connections from clients and we see many errors related to connections being forcibly closed.
We see two cases where this occurs, the former of which occurs much more often.
```
Dec 29 01:12:43.909934 tlx-dal-ecv2-staging kamailio_edge[14813]: WARNING: websocket [ws_frame.c:810]: ws_keepalive(): forcibly closing connection
Dec 29 01:12:43.910179 tlx-dal-ecv2-staging kamailio_edge[14813]: ERROR: websocket [ws_conn.c:375]: wsconn_close_now(): getting TCP/TLS connection while trying to close. src_ip:src_port=x.x.x.x:49319, dst_port=443
```
```
Dec 29 00:53:28.110949 tlx-dal-ecv2-staging kamailio_edge[14817]: WARNING: websocket [ws_frame.c:227]: encode_and_send_ws_frame(): TCP/TLS connection get failed
Dec 29 00:53:28.111187 tlx-dal-ecv2-staging kamailio_edge[14817]: ERROR: websocket [ws_frame.c:761]: ping_pong(): sending keepalive. src_ip:src_port=x.x.x.x:46712, dst_port=443
```

### Troubleshooting
There seems to be a common occurrence where the WebSocket keepalive will not receive a pong and close the websocket connection. While closing, we see that the underlying TCP connection has already been closed. While that may be harmless, I am concerned there is a race condition that could lead to other problems.

### Additional Information

  * **Kamailio Version** - output of `kamailio -v`

```
version: kamailio 5.3.1 (x86_64/linux) d68f5c
flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED
ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB
poll method support: poll, epoll_lt, epoll_et, sigio_rt, select.
id: d68f5c
compiled on 07:32:16 Dec 29 2021 with gcc 8.3.0
```

* **Operating System**:

<!--
Details about the operating system, the type: Linux (e.g.,: Debian 8.4, Ubuntu 16.04, CentOS 7.1, ...), MacOS, xBSD, Solaris, ...;
Kernel details (output of `lsb_release -a` and `uname -a`)
-->

```
> lsb_release -a
No LSB modules are available.
Distributor ID:	Debian
Description:	Debian GNU/Linux 10 (buster)
Release:	10
Codename:	buster

> uname -a
Linux tlx-dal-ecv2-staging 4.19.0-8-amd64 #1 SMP Debian 4.19.98-1 (2020-01-26) x86_64 GNU/Linux
```


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