ext4: Rename and document EXT4_EX_FILTER to EXT4_EX_QUERY_FILTER

Rename EXT4_EX_FILTER to EXT4_EX_QUERY_FILTER to better describe its
purpose as a filter mask used specifically in ext4_map_query_blocks().
Add a comment explaining that this macro is used to filter flags needed
when querying the on-disk extent tree.

We will later use EXT4_EX_QUERY_FILTER mask to add another
EXT4_GET_BLOCKS_QUERY needed to lookup in on-disk extent tree.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://patch.msgid.link/51f05d0ba286372eb8693af95bd4b10194b53141.1747677758.git.ritesh.list@gmail.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>