selftests/bpf: test_xsk: Split xskxceiver

AF_XDP features are tested by the test_xsk.sh script but not by the
test_progs framework. The tests used by the script are defined in
xksxceiver.c which can't be integrated in the test_progs framework as is.

Extract these test definitions from xskxceiver{.c/.h} to put them in new
test_xsk{.c/.h} files.
Keep the main() function and its unshared dependencies in xksxceiver to
avoid impacting the test_xsk.sh script which is often used to test real
hardware.

Signed-off-by: Bastien Curutchet (eBPF Foundation) <[email protected]>

Author: bastien-curutchet

tools/testing/selftests/bpf/Makefile

@@ -777,7 +777,7 @@ $(OUTPUT)/test_verifier: test_verifier.c verifier/tests.h $(BPFOBJ) | $(OUTPUT)
 
 # Include find_bit.c to compile xskxceiver.
 EXTRA_SRC := $(TOOLSDIR)/lib/find_bit.c
-$(OUTPUT)/xskxceiver: $(EXTRA_SRC) xskxceiver.c xskxceiver.h $(OUTPUT)/network_helpers.o $(OUTPUT)/xsk.o $(OUTPUT)/xsk_xdp_progs.skel.h $(BPFOBJ) | $(OUTPUT)
+$(OUTPUT)/xskxceiver: $(EXTRA_SRC) test_xsk.c test_xsk.h xskxceiver.c xskxceiver.h $(OUTPUT)/network_helpers.o $(OUTPUT)/xsk.o $(OUTPUT)/xsk_xdp_progs.skel.h $(BPFOBJ) | $(OUTPUT)
 	$(call msg,BINARY,,$@)
 	$(Q)$(CC) $(CFLAGS) $(filter %.a %.o %.c,$^) $(LDLIBS) -o $@