PX30_Android8.1默认3G移动网络改为默认4G移动网络

修改路径：px30_android-8.1\frameworks\base\telephony\java\com\android\internal\telephony
修改文件：RILConstants.java

修改内容：

NETWORK_MODE_LTE_TDSCDMA_GSM_WCDMA   = 20; /* TD-SCDMA, GSM/WCDMA and LTE */
    int NETWORK_MODE_TDSCDMA_CDMA_EVDO_GSM_WCDMA  = 21; /*TD-SCDMA,EvDo,CDMA,GSM/WCDMA*/
    int NETWORK_MODE_LTE_TDSCDMA_CDMA_EVDO_GSM_WCDMA = 22; /* TD-SCDMA/LTE/GSM/WCDMA, CDMA, and EvDo */
    int PREFERRED_NETWORK_MODE      = SystemProperties.getInt("ro.telephony.default_network",
             NETWORK_MODE_LTE_GSM_WCDMA); /*默认4G网络*/
			 /*NETWORK_MODE_WCDMA_PREF);*//*默认3G网络*/
            
    int BAND_MODE_UNSPECIFIED = 0;      //"unspecified" (selected by baseband automatically)
    int BAND_MODE_EURO = 1;             //"EURO band" (GSM-900 / DCS-1800 / WCDMA-IMT-2000)