[posix] add platformNetifDeinit (#4726)

Close netif file descriptors to re-open after reset.

src/posix/platform/netif.cpp

@@ -384,6 +384,29 @@ exit:
     return;
 }
 
+void platformNetifDeinit(void)
+{
+    if (sTunFd != -1)
+    {
+        close(sTunFd);
+        sTunFd = -1;
+    }
+
+    if (sIpFd != -1)
+    {
+        close(sIpFd);
+        sIpFd = -1;
+    }
+
+    if (sNetlinkFd != -1)
+    {
+        close(sNetlinkFd);
+        sNetlinkFd = -1;
+    }
+
+    sTunIndex = 0;
+}
+
 void platformNetifInit(otInstance *aInstance, const char *aInterfaceName)
 {
     struct ifreq ifr;

src/posix/platform/platform-posix.h

@@ -217,6 +217,12 @@ void platformRadioInit(const otPlatformConfig *aPlatformConfig);
  */
 void platformRadioDeinit(void);
 
+/**
+ * This function shuts down platform network interface.
+ *
+ */
+void platformNetifDeinit(void);
+
 /**
  * This function inputs a received radio frame.
  *

src/posix/platform/system.cpp

@@ -73,6 +73,9 @@ void otSysDeinit(void)
     virtualTimeDeinit();
 #endif
     platformRadioDeinit();
+#if OPENTHREAD_CONFIG_PLATFORM_NETIF_ENABLE
+    platformNetifDeinit();
+#endif
 }
 
 #if OPENTHREAD_POSIX_VIRTUAL_TIME