fsck.gfs2: Further performance gains with function valid_block_ip
    
    Before this patch, many functions in fsck.gfs2 checked for blocks
    being valid. To check if a block is valid, you really need to check
    that it's inside the area covered by a valid resource group. For
    example, if a data block is pointing to a rgrp bitmap block, that's
    invalid. To achieve this, it does a rgrp search, which traverses
    the rgrp tree. This patch optimizes that by allowing functions to
    pass in the ip pointer, so like before, we can check if that rgrp
    covers the block in question and save ourselves a lot of work
    traversing the tree.
    
    Signed-off-by: Bob Peterson <rpeterso@redhat.com>