bpf: selftests: Specify CONFIG_DYNAMIC_FTRACE in the testing config

The tracing test and the recent kfunc call test require
CONFIG_DYNAMIC_FTRACE.  This patch adds it to the config file.
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210403002921.3419721-1-kafai@fb.com

tools/testing/selftests/bpf/config

@@ -44,3 +44,5 @@ CONFIG_SECURITYFS=y
 CONFIG_IMA_WRITE_POLICY=y
 CONFIG_IMA_READ_POLICY=y
 CONFIG_BLK_DEV_LOOP=y
+CONFIG_FUNCTION_TRACER=y
+CONFIG_DYNAMIC_FTRACE=y