Add Wisun Fan device extended key usage

Add the Wisun extended key usage oid and tests.
diff --git a/library/oid.c b/library/oid.c
index 4e10f8a..8059a33 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -284,12 +284,13 @@
 
 static const mbedtls_oid_descriptor_t oid_ext_key_usage[] =
 {
-    { ADD_LEN( MBEDTLS_OID_SERVER_AUTH ),      "id-kp-serverAuth",      "TLS Web Server Authentication" },
-    { ADD_LEN( MBEDTLS_OID_CLIENT_AUTH ),      "id-kp-clientAuth",      "TLS Web Client Authentication" },
-    { ADD_LEN( MBEDTLS_OID_CODE_SIGNING ),     "id-kp-codeSigning",     "Code Signing" },
-    { ADD_LEN( MBEDTLS_OID_EMAIL_PROTECTION ), "id-kp-emailProtection", "E-mail Protection" },
-    { ADD_LEN( MBEDTLS_OID_TIME_STAMPING ),    "id-kp-timeStamping",    "Time Stamping" },
-    { ADD_LEN( MBEDTLS_OID_OCSP_SIGNING ),     "id-kp-OCSPSigning",     "OCSP Signing" },
+    { ADD_LEN( MBEDTLS_OID_SERVER_AUTH ),      "id-kp-serverAuth",       "TLS Web Server Authentication" },
+    { ADD_LEN( MBEDTLS_OID_CLIENT_AUTH ),      "id-kp-clientAuth",       "TLS Web Client Authentication" },
+    { ADD_LEN( MBEDTLS_OID_CODE_SIGNING ),     "id-kp-codeSigning",      "Code Signing" },
+    { ADD_LEN( MBEDTLS_OID_EMAIL_PROTECTION ), "id-kp-emailProtection",  "E-mail Protection" },
+    { ADD_LEN( MBEDTLS_OID_TIME_STAMPING ),    "id-kp-timeStamping",     "Time Stamping" },
+    { ADD_LEN( MBEDTLS_OID_OCSP_SIGNING ),     "id-kp-OCSPSigning",      "OCSP Signing" },
+    { ADD_LEN( MBEDTLS_OID_WISUN_FAN ),        "id-kp-wisun-fan-device", "Wi-SUN Alliance Field Area Network (FAN)" },
     { NULL, 0, NULL, NULL },
 };