selftests/net: fix uninitialized variables

When building with clang, via:

    make LLVM=1 -C tools/testing/selftest

...clang warns about three variables that are not initialized in all
cases:

1) The opt_ipproto_off variable is used uninitialized if "testname" is
not "ip". Willem de Bruijn pointed out that this is an actual bug, and
suggested the fix that I'm using here (thanks!).

2) The addr_len is used uninitialized, but only in the assert case,
   which bails out, so this is harmless.

3) The family variable in add_listener() is only used uninitialized in
   the error case (neither IPv4 nor IPv6 is specified), so it's also
   harmless.

Fix by initializing each variable.
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20240506190204.28497-1-jhubbard@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/gro.c

@@ -119,6 +119,9 @@ static void setup_sock_filter(int fd)
 		next_off = offsetof(struct ipv6hdr, nexthdr);
 	ipproto_off = ETH_HLEN + next_off;
 
+	/* Overridden later if exthdrs are used: */
+	opt_ipproto_off = ipproto_off;
+
 	if (strcmp(testname, "ip") == 0) {
 		if (proto == PF_INET)
 			optlen = sizeof(struct ip_timestamp);

tools/testing/selftests/net/ip_local_port_range.c

@@ -359,7 +359,7 @@ TEST_F(ip_local_port_range, late_bind)
 		struct sockaddr_in v4;
 		struct sockaddr_in6 v6;
 	} addr;
-	socklen_t addr_len;
+	socklen_t addr_len = 0;
 	const int one = 1;
 	int fd, err;
 	__u32 range;

tools/testing/selftests/net/mptcp/pm_nl_ctl.c

@@ -1276,7 +1276,7 @@ int add_listener(int argc, char *argv[])
 	struct sockaddr_storage addr;
 	struct sockaddr_in6 *a6;
 	struct sockaddr_in *a4;
-	u_int16_t family;
+	u_int16_t family = AF_UNSPEC;
 	int enable = 1;
 	int sock;
 	int err;