The reservation for the various forms of inode allocation is
scattered across several different functions. This includes two
variants of chunk allocation (v5 icreate transactions vs. older
create transactions) and the inode free transaction.

To clean up some of this code and clarify the purpose of specific
allocfree reservations, continue the pattern of defining helper
functions for smaller operational units of broader transactions.
Refactor the reservation into an inode chunk alloc/free helper that
considers the various conditions based on filesystem format.

An inode chunk free involves an extent free and buffer
invalidations. The latter requires reservation for log headers only.
An inode chunk allocation modifies the free space btrees and logs
the chunk on v4 supers. v5 supers initialize the inode chunk using
ordered buffers and so do not log the chunk.

As a side effect of this refactoring, add one more allocfree res to
the ifree transaction. Technically this does not serve a specific
purpose because inode chunks are freed via deferred operations and
thus occur after a transaction roll. tr_ifree has a bit of a history
of tx overruns caused by too many agfl fixups during sustained file
deletion workloads, so add this extra reservation as a form of
padding nonetheless.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>