tsnep: Support XDP BPF program setup

Implement setup of BPF programs for XDP RX path with command
XDP_SETUP_PROG of ndo_bpf(). This is the final step for XDP RX path
support.

There is no need to reinit the RX queues as they are always prepared for
XDP.

Additionally remove $(tsnep-y) from $(tsnep-objs) because it is added
automatically.

Test results with A53 1.2GHz:

XDP_DROP (samples/bpf/xdp1)
proto 17:     883878 pkt/s

XDP_TX (samples/bpf/xdp2)
proto 17:     255693 pkt/s

XDP_REDIRECT (samples/bpf/xdpsock)
 sock0@eth2:0 rxdrop xdp-drv
                   pps            pkts           1.00
rx                 855,582        5,404,523
tx                 0              0

XDP_REDIRECT (samples/bpf/xdp_redirect)
eth2->eth1         613,267 rx/s   0 err,drop/s   613,272 xmit/s

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>