net/af_xdp: support shared UMEM

net/af_xdp: support shared UMEM

Kernel v5.10 will introduce the ability to efficiently share a UMEM
between AF_XDP sockets bound to different queue ids on the same or
different devices. This patch integrates that functionality into the AF_XDP
PMD.

A PMD will attempt to share a UMEM with others if the shared_umem=1 vdev
arg is set. UMEMs can only be shared across PMDs with the same mempool, up
to a limited number of PMDs goverened by the size of the given mempool.
Sharing UMEMs is not supported for non-zero-copy (aligned) mode.

The benefit of sharing UMEM across PMDs is a saving in memory due to not
having to register the UMEM multiple times. Throughput was measured to
remain within 2% of the default mode (not sharing UMEM).

A version of libbpf >= v0.2.0 is required and the appropriate pkg-config
file for libbpf must be installed such that meson can determine the
version.

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>