page_pool: add page_pool_dev_alloc_netmem()

Similarly to other _dev shorthands, add one for page_pool_alloc_netmem()
to allocate a netmem using the default Rx GFP flags (ATOMIC | NOWARN) to
make the page -> netmem transition of drivers easier.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Link: https://patch.msgid.link/20241218174435.1445282-2-aleksander.lobakin@intel.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>