Add methods to set/get connection PHY's.

* Added `NimBLEDevice::setDefaultPhy` which will set the default preferred PHY for all connections.
* Added `NimBLEClient::updatePhy` to request a PHY change with a peer.
* Added `NimBLEClient::getPhy` to read the current connection PHY setting.
* Added `NimBLEServer::updatePhy` to request a PHY change with a peer.
* Added `NimBLEServer::getPhy` to read the PHY of a peer connection.
* Added callbacks:
* - `NimBLEClientCallbacks::onPhyUpdate`
* - `NimBLEServerCallbacks::onPhyUpdate`
 Which are called when the PHY update is complete.

src/NimBLEDevice.h

@@ -136,6 +136,10 @@ class NimBLEDevice {
     static void          onSync(void);
     static void          host_task(void* param);
 
+# if CONFIG_BT_NIMBLE_EXT_ADV
+    static bool setDefaultPhy(uint8_t txPhyMask, uint8_t rxPhyMask);
+# endif
+
 # if defined(CONFIG_BT_NIMBLE_ROLE_OBSERVER)
     static NimBLEScan* getScan();
 # endif