Merge branch 'xdp-a-fistful-of-generic-changes-pt-iii'

Alexander Lobakin says:

====================
xdp: a fistful of generic changes pt. III

XDP for idpf is currently 5.(6) chapters:
* convert Rx to libeth;
* convert Tx and stats to libeth;
* generic XDP and XSk code changes;
* generic XDP and XSk code additions pt. 1;
* generic XDP and XSk code additions pt. 2 (you are here);
* actual XDP for idpf via new libeth_xdp;
* XSk for idpf (via ^).

Part III.3 does the following:
* adds generic functions to build skbs from xdp_buffs (regular and
  XSk) and attach frags to xdp_buffs (regular and XSk);
* adds helper to optimize XSk xmit in drivers.

Everything is prereq for libeth_xdp, but will be useful standalone
as well: less code in drivers, faster XSk XDP_PASS, smaller object
code.
====================

Link: https://patch.msgid.link/20241218174435.1445282-1-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>