PDUEncoding->UserData编码和解码方式不一致

get使用的是直接通过char转换，
set使用的是BigEndianUnicode
虽然对于UNICODE码没有问题，但对于不在UNICODE编码范围的字符
(D800-DFFF)，结果会不一致。
测试代码如下：
            int high = 0;
            string s1;
            StringBuilder sb = new StringBuilder();
            for (; high < 0x100; high ++)
            {
                s1 = String.Empty;
                sb.Clear();
                int low = 0;
                for (; low < 0x100; low++)
                {
                    sb.Append((char)(low|(high << 8)));
                }
                s1 = sb.ToString();
                _p.UserData = s1;
                string s2 = _p.UserData;
                Assert.AreEqual(s1, s2);//测试到 high = 0xD8 出错
            }

Original issue reported on code.google.com by hiheart...@gmail.com on 6 Dec 2012 at 1:57

webo001 / gsmmodem

PDUEncoding->UserData编码和解码方式不一致 #17