Only test ManuFDB when available

test/regression.uts

@@ -656,11 +656,17 @@ send_and_sniff(Ether()/IP(dst="secdev.org")/ICMP())
 
 = __repr__
 
-conf.manufdb
+if conf.manufdb:
+    conf.manufdb
+else:
+    True
 
 = check _resolve_MAC
 
-assert conf.manufdb._resolve_MAC("00:00:63") == "HP"
+if conf.manufdb:
+    assert conf.manufdb._resolve_MAC("00:00:63") == "HP"
+else:
+    True
 
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