tests/Makefile.am: do not add files to EXTRA_DIST conditionally

These files must be present in the release tarballs regardless
of the configure options (ENABLE_LIBSCTP, ENABLE_SCTP_TESTS).

Change-Id: I8f530d6157b00907dd1b438100bb0fb300dfcd22
Related: OS#6349
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 5042b3c..7c109a1 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -504,11 +504,11 @@
 	     osmo_io/osmo_io_test.ok osmo_io/osmo_io_test.err \
 	     soft_uart/soft_uart_test.ok \
 	     rlp/rlp_test.ok \
+	     socket/socket_sctp_test.ok socket/socket_sctp_test.err \
 	     $(NULL)
 
 if ENABLE_LIBSCTP
 if ENABLE_SCTP_TESTS
-EXTRA_DIST += socket/socket_sctp_test.ok socket/socket_sctp_test.err
 check_PROGRAMS += socket/socket_sctp_test
 socket_socket_sctp_test_SOURCES = socket/socket_sctp_test.c
 endif