test/test_addpfx.c: Fix declaration of pfxmultab (#428)

This was causing test failures on Debian's s390x architecture.

Author: df7cb

test/test_addpfx.c

@@ -6,7 +6,7 @@
 // OBJECT ../src/addpfx.o
 // OBJECT ../src/bands.o
 
-extern int pfxmultab;
+extern bool pfxmultab;
 
 int find_worked_pfx(char *prefix);