net: fix test_bpf build to depend on NET

Fix build when CONFIG_NET is not enabled.
Fixes these build errors:

WARNING: "sk_unattached_filter_destroy" [lib/test_bpf.ko] undefined!
WARNING: "kfree_skb" [lib/test_bpf.ko] undefined!
WARNING: "sk_unattached_filter_create" [lib/test_bpf.ko] undefined!
WARNING: "sk_run_filter_int_skb" [lib/test_bpf.ko] undefined!
WARNING: "__alloc_skb" [lib/test_bpf.ko] undefined!

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/Kconfig.debug

@@ -1623,7 +1623,7 @@ config TEST_USER_COPY
 config TEST_BPF
 	tristate "Test BPF filter functionality"
 	default n
-	depends on m
+	depends on m && NET
 	help
 	  This builds the "test_bpf" module that runs various test vectors
 	  against the BPF interpreter or BPF JIT compiler depending on the