tests: net: mgmt: define request handler properly

Define the request handler properly within the net mgmt test. This is
required for the alias() attribute to work correctly with clang. Also,
correct the handler signature to use size_t as expected. This resolves a
test failure seen with clang when building the net mgmt test for
native_sim.

Signed-off-by: Daniel DeGrasse <ddegrasse@tenstorrent.com>

tests/net/mgmt/src/mgmt.c

@@ -49,8 +49,10 @@ static struct in6_addr addr6 = { { { 0xfe, 0x80, 0, 0, 0, 0, 0, 0,
 
 static char info_data[TEST_MGMT_EVENT_INFO_SIZE];
 
-static int test_mgmt_request(uint64_t mgmt_request,
-			     struct net_if *iface, void *data, uint32_t len)
+NET_MGMT_DEFINE_REQUEST_HANDLER(TEST_MGMT_REQUEST);
+
+static int test_mgmt_request(uint64_t mgmt_req,
+			     struct net_if *iface, void *data, size_t len)
 {
 	uint32_t *test_data = data;