Issue in UDP management for BG96

[gpaquet85]

Describe the bug
When I tried to send data with mqtt_publisher sample, an error was raised in BG96 driver.
It is not possible to sart MQTT (TCP) connection

To Reproduce
Build samples/net/mqtt_publisher

1. west build -p auto -b rak5010_nrf52840 samples/net/mqtt_publisher
2. west flash
   Error is clearly raised because it is impossible to connect to MQTT broker

Expected behavior
It is expected that MQTT sample is working as it is tested.
Moreover comment in driver says : /* UDP is not supported. */
and code is : if (sock->ip_proto != IPPROTO_UDP)
so it is not in line.

Impact
Not any TCP connection possible at this state

Logs and console output
I can add Log and console output if necessary. Just for information, I created PR to fix this.

Environment:

• OS: Linux
• Toolchain: Zephyr SDK
• Commit SHA: 3befd7d

Additional context
Tested on two different boards with two BG96.

[gpaquet85]

Linked to this PR: #31317