core:sr_module.c increased number of pre-allocated static buffers in get_str_fparam()

Increased the number from 3 to 6 as more are needed by modules like carrierroute when avp's are used as function parameters
(Bug reported by Ole Kaas)
(cherry picked from commit 4fd1e775f701d79d1d7f5e75bd7ff621739914b5)

sr_module.c

@@ -1415,7 +1415,7 @@ int fixup_str_2(void** param, int param_no)
 
 
 #define PV_PRINT_BUF_SIZE  1024
-#define PV_PRINT_BUF_NO    3
+#define PV_PRINT_BUF_NO    6
 /** Get the function parameter value as string.
  *  @return  0 - Success
  *          -1 - Cannot get value