net: openthread: add log_strdup to role text, fix doc gender issue

- Add a `log_strdup` to the role text output for logging V1
  compatibility
- Fix style issues
- Change where the documentation refers to an OpenThread device as
  "himself" to "itself"

Signed-off-by: Chris Pearson <[email protected]>

Author: pearson

samples/net/lwm2m_client/README.rst

@@ -214,7 +214,7 @@ networking do the following:
    :compact:
 
 Note: If not provisioned (fully erased before flash), device will form
-new OpenThread network and promote himself as leader (Current role: leader).
+new OpenThread network and promote itself to leader (Current role: leader).
 To join into already existing OT network, either enable CONFIG_OPENTHREAD_JOINER=y
 and CONFIG_OPENTHREAD_JOINER_AUTOSTART=y and send join request from other
 already joined device with joiner capabilities, or provision it manually

subsys/net/l2/openthread/openthread.c

@@ -169,7 +169,9 @@ static void ot_state_changed_handler(uint32_t flags, void *context)
 	struct openthread_context *ot_context = context;
 
 	NET_INFO("State changed! Flags: 0x%08" PRIx32 " Current role: %s",
-		 flags, otThreadDeviceRoleToString( otThreadGetDeviceRole(ot_context->instance)));
+		flags,
+		log_strdup(otThreadDeviceRoleToString(otThreadGetDeviceRole(ot_context->instance)))
+		);
 
 	if (flags & OT_CHANGED_IP6_ADDRESS_REMOVED) {
 		NET_DBG("Ipv6 address removed");