net/af_xdp: mark recvfrom return as ignored

net/af_xdp: mark recvfrom return as ignored

Coverity complains that the return value of recvfrom() in the AF_XDP
datapath is not checked. We don't care about the return value because in
the case of an error we still return 0 from the receive function to
indicate no packets were received. So to make Coverity happy we cast the
return to 'void'.

Coverity issue: 369671
Fixes: 63e8989fe5a4 ("net/af_xdp: use recvfrom instead of poll syscall")

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