net: page_pool: Add page_pool_put_page_bulk() to page_pool.rst

Introduce page_pool_put_page_bulk() entry into the API section of
page_pool.rst
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/a6a5141b4d7b7b71fa7778b16b48f80095dd3233.1606146163.git.lorenzo@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/page_pool.rst

@@ -97,6 +97,14 @@ a page will cause no race conditions is enough.
 
 * page_pool_get_dma_dir(): Retrieve the stored DMA direction.
 
+* page_pool_put_page_bulk(): Tries to refill a number of pages into the
+  ptr_ring cache holding ptr_ring producer lock. If the ptr_ring is full,
+  page_pool_put_page_bulk() will release leftover pages to the page allocator.
+  page_pool_put_page_bulk() is suitable to be run inside the driver NAPI tx
+  completion loop for the XDP_REDIRECT use case.
+  Please note the caller must not use data area after running
+  page_pool_put_page_bulk(), as this function overwrites it.
+
 Coding examples
 ===============