The check in f2f5130fefbe24488e2a303d2d029e81e1e06198 needs to be adjusted to include FFmpeg 6 (see [here](https://github.com/FFmpeg/FFmpeg/blob/n6.1.1/libavformat/version_major.h#L48)).

Error:

```c
filters/ff_mx.c:298:26: error: incompatible function pointer types passing 'int (*)(void *, const uint8_t *, int)' (aka 'int (*)(void *, const unsigned char *, int)') to parameter of type 'int (*)(void *, uint8_t *, int)' (aka 'int (*)(void *, unsigned char *, int)') [-Wincompatible-function-pointer-types]
                                                                          1, ctx, NULL, &ffavio_write_packet, &ffavio_seek);
```
Fails to build with FFmpeg 6
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Fails to build with FFmpeg 6
Issue date:

--- start body ---
The check in f2f5130fefbe24488e2a303d2d029e81e1e06198 needs to be adjusted to include FFmpeg 6 (see [here](https://github.com/FFmpeg/FFmpeg/blob/n6.1.1/libavformat/version_major.h#L48)).

Error:

```c
filters/ff_mx.c:298:26: error: incompatible function pointer types passing 'int (*)(void *, const uint8_t *, int)' (aka 'int (*)(void *, const unsigned char *, int)') to parameter of type 'int (*)(void *, uint8_t *, int)' (aka 'int (*)(void *, unsigned char *, int)') [-Wincompatible-function-pointer-types]
                                                                          1, ctx, NULL, &ffavio_write_packet, &ffavio_seek);
```
--- end body ---
