fuzz: commit test case for oss-fuzz issue 6884

This seems to be a false positive in msan:
https://github.com/google/sanitizers/issues/767.

I don't see anything wrong with the code either, and valgrind does not see the
issue. Anyway, let's add the test case.

We don't have msan hooked up yet, but hopefully we'll in the future.

oss-fuzz #6884.

src/test/test-socket-util.c

@@ -118,6 +118,9 @@ static void test_socket_address_parse_netlink(void) {
         assert_se(socket_address_parse_netlink(&a, "route 10") >= 0);
         assert_se(a.sockaddr.sa.sa_family == AF_NETLINK);
         assert_se(a.protocol == NETLINK_ROUTE);
+
+        /* oss-fuzz #6884 */
+        assert_se(socket_address_parse_netlink(&a, "\xff") < 0);
 }
 
 static void test_socket_address_equal(void) {

test/fuzz-regressions/fuzz-unit-file/oss-fuzz-6884

@@ -0,0 +1,3 @@
+socket
+[Socket]
+ListenNetlink=ÿ

test/fuzz-regressions/meson.build

@@ -29,4 +29,5 @@ sanitizers = [['address', sanitize_address]]
 fuzz_regression_tests = '''
         fuzz-dns-packet/oss-fuzz-5465
         fuzz-dns-packet/issue-7888
+        fuzz-unit-file/oss-fuzz-6884
 '''.split()