CVE-2023-54121 btrfs: fix incorrect splitting in btrfs_drop_extent_map_range

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix incorrect splitting in btrfsdropextentmaprange In production we were seeing a variety of WARNON's in the extentmap code, specifically in btrfsdropextentmaprange when we have to call addextentmapping for our second spli...