btrfs: output extra debug info if we failed to find an inline backref

In the Linux kernel, the following vulnerability has been resolved:

btrfs: output extra debug info if we failed to find an inline backref

[BUG]

Syzbot reported several warning triggered inside

lookup_inline_extent_backref().

[CAUSE]

As usual, the reproducer doesn't reliably trigger locally here, but at

least we know the WARN_ON() is triggered when an inline backref can not

be found, and it can only be triggered when @insert is true. (I.e.

inserting a new inline backref, which means the backref should already

exist)

[ENHANCEMENT]

After the WARN_ON(), dump all the parameters and the extent tree

leaf to help debug.