Merge branch 'net-consolidate-page_is_pfmemalloc-usage'

Alexander Lobakin says:

====================
net: consolidate page_is_pfmemalloc() usage

page_is_pfmemalloc() is used mostly by networking drivers to test
if a page can be considered for reusing/recycling.
It doesn't write anything to the struct page itself, so its sole
argument can be constified, as well as the first argument of
skb_propagate_pfmemalloc().
In Page Pool core code, it can be simply inlined instead.
Most of the callers from NIC drivers were just doppelgangers of
the same condition tests. Derive them into a new common function
do deduplicate the code.

Resend of v3 [2]:
 - it missed Patchwork and Netdev archives, probably due to server-side
   issues.

Since v2 [1]:
 - use more intuitive name for the new inline function since there's
   nothing "reserved" in remote pages (Jakub Kicinski, John Hubbard);
 - fold likely() inside the helper itself to make driver code a bit
   fancier (Jakub Kicinski);
 - split function introduction and using into two separate commits;
 - collect some more tags (Jesse Brandeburg, David Rientjes).

Since v1 [0]:
 - new: reduce code duplication by introducing a new common function
   to test if a page can be reused/recycled (David Rientjes);
 - collect autographs for Page Pool bits (Jesper Dangaard Brouer,
   Ilias Apalodimas).

[0] https://lore.kernel.org/netdev/20210125164612.243838-1-alobakin@pm.me
[1] https://lore.kernel.org/netdev/20210127201031.98544-1-alobakin@pm.me
[2] https://lore.kernel.org/lkml/20210131120844.7529-1-alobakin@pm.me
====================

Link: https://lore.kernel.org/r/20210202133030.5760-1-alobakin@pm.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>