Make pri_pres2str() return correct string.

* Fix pri_pres2str() mask creation.

(closes issue PRI-139)
Reported by: Pavel Troller
Patches:
      q931.c.diff (license #6302) patch uploaded by Pavel Troller


git-svn-id: https://origsvn.digium.com/svn/libpri/branches/1.4@2286 2fbb986a-6c06-0410-b554-c9c1f0a7f128

q931.c

@@ -2068,7 +2068,7 @@ char *pri_pres2str(int pres)
 		{ PRI_PRES_RESERVED | PRI_PRES_NETWORK_NUMBER,               "Reserved, Network provided" },
 	};
 
-	pres &= (PRI_PRES_RESTRICTION & PRI_PRES_NUMBER_TYPE);
+	pres &= (PRI_PRES_RESTRICTION | PRI_PRES_NUMBER_TYPE);
 	return code2str(pres, press, sizeof(press) / sizeof(press[0]));
 }