drivers/bluetooth/hci/userchan.c build waring w gcc13

[aescolar]

Describe the bug
drivers/bluetooth/hci/userchan.c builds with a warning w gcc13,
as it seems to believe the number of read bytes may overflow the frame_size type.

Note gcc 13 is the default w Ubuntu 24.04

To Reproduce
Steps to reproduce the behavior (w gcc 13)

1. mkdir build; cd build
2. cmake -GNinja -DBOARD=native_sim ../samples/hello_world/ -DCONFIG_BT=y
3. ninja
4. See error

Expected behavior
No build warning

Impact
Failing twister tests (~20), build warning when using this driver

Logs and console output

In file included from ...
                 from zephyr/include/zephyr/types.h:11,
                 from zephyr/include/zephyr/kernel_includes.h:21,
                 from zephyr/include/zephyr/kernel.h:17,
                 from zephyr/drivers/bluetooth/hci/userchan.c:9:
In function ‘read’,
    inlined from ‘rx_thread’ at drivers/bluetooth/hci/userchan.c:201:9: /usr/include/i386-linux-gnu/bits/unistd.h:28:10: warning: ‘__read_alias’ specified size between 4294902273 and 4294967295 exceeds maximum object size 2147483647 [-Wstringop-overflow=]
   28 |   return __glibc_fortify (read, __nbytes, sizeof (char),
      |          ^~~~~~~~~~~~~~~
drivers/bluetooth/hci/userchan.c: In function ‘rx_thread’: drivers/bluetooth/hci/userchan.c:187:32: note: destination object allocated here
  187 |                 static uint8_t frame[512];
      |                                ^~~~~
/usr/include/i386-linux-gnu/bits/unistd-decl.h:29:16: note: in a call to function ‘__read_alias’ declared with attribute ‘access (write_only, 2, 3)’
   29 | extern ssize_t __REDIRECT_FORTIFY (__read_alias, (int __fd, void *__buf,
      |                ^~~~~~~~~~~~~~~~~~

Environment (please complete the following information):

• OS: Linux, Ubuntu 24.04
• Toolchain: Host gcc 13
• Commit SHA or Version used: main as of now a747d1a