pgsql: Rename BufferAccessStrategyData.ring_size to nbuffers

Rename BufferAccessStrategyData.ring_size to nbuffers

The new name better reflects what the field is - the size of the buffers[]
array.  ring_size sounded more like it is in units of bytes.

An upcoming commit allows a BufferAccessStrategy of custom sizes, so it
seems relevant to improve this beforehand.

Author: Melanie Plageman
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/CAAKRu_YefVbhg4rAxU2frYFdTap61UftH-kUNQZBvAs%2BYK81Zg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8d928e3a9fe7577e7abf2388b60cc67ed94f6d24

Modified Files
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src/backend/storage/buffer/freelist.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)