slot: shorten slot type

Create an alias `sdbusplus::slot_t` to `sdbusplus::slot::slot`
to reduce duplication.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I0ac45f676f1e52f53b6ea3a5b487d0f183641e37
diff --git a/include/sdbusplus/bus/match.hpp b/include/sdbusplus/bus/match.hpp
index be391b2..5763e96 100644
--- a/include/sdbusplus/bus/match.hpp
+++ b/include/sdbusplus/bus/match.hpp
@@ -79,7 +79,7 @@
     {}
 
   private:
-    slot::slot _slot;
+    slot_t _slot;
     std::unique_ptr<callback_t> _callback = nullptr;
 
     static int callCallback(sd_bus_message* m, void* context,
diff --git a/include/sdbusplus/message.hpp b/include/sdbusplus/message.hpp
index a3f95af..7bd84a8 100644
--- a/include/sdbusplus/message.hpp
+++ b/include/sdbusplus/message.hpp
@@ -414,7 +414,7 @@
      *  @return The slot handle that manages the lifetime of the call object.
      */
     template <typename Cb>
-    [[nodiscard]] slot::slot
+    [[nodiscard]] slot_t
         call_async(Cb&& cb, std::optional<SdBusDuration> timeout = std::nullopt)
     {
         sd_bus_slot* slot;
@@ -427,7 +427,7 @@
         {
             throw exception::SdBusError(-r, "sd_bus_call_async");
         }
-        slot::slot ret(std::move(slot));
+        slot_t ret(std::move(slot));
         if constexpr (std::is_pointer_v<CbT>)
         {
             _intf->sd_bus_slot_set_userdata(slot, reinterpret_cast<void*>(cb));
diff --git a/include/sdbusplus/server/interface.hpp b/include/sdbusplus/server/interface.hpp
index d840bd2..4e709ea 100644
--- a/include/sdbusplus/server/interface.hpp
+++ b/include/sdbusplus/server/interface.hpp
@@ -110,7 +110,7 @@
     bus_t _bus;
     std::string _path;
     std::string _interf;
-    slot::slot _slot;
+    slot_t _slot;
     SdBusInterface* _intf;
     bool _interface_added;
 };
diff --git a/include/sdbusplus/server/manager.hpp b/include/sdbusplus/server/manager.hpp
index 2a71127..9241bd9 100644
--- a/include/sdbusplus/server/manager.hpp
+++ b/include/sdbusplus/server/manager.hpp
@@ -41,7 +41,7 @@
      *  @param[in] bus - The bus to register on.
      *  @param[in] path - The path to register.
      */
-    manager(sdbusplus::bus_t& bus, const char* path) : _slot(nullptr)
+    manager(sdbusplus::bus_t& bus, const char* path)
     {
         sd_bus_slot* slot = nullptr;
         sdbusplus::SdBusInterface* intf = bus.getInterface();
@@ -52,7 +52,7 @@
     }
 
   private:
-    slot::slot _slot;
+    slot_t _slot{nullptr};
 };
 
 } // namespace manager
diff --git a/include/sdbusplus/slot.hpp b/include/sdbusplus/slot.hpp
index 27f4a70..5fa9141 100644
--- a/include/sdbusplus/slot.hpp
+++ b/include/sdbusplus/slot.hpp
@@ -73,4 +73,7 @@
 };
 
 } // namespace slot
+
+using slot_t = slot::slot;
+
 } // namespace sdbusplus