Grandstream HT502 ATA Firmware

BUG FIXES:

- Fixed Time zone "GMT+12:00 (Auckland, Wellington)" shows wrong time
- Updated New Zealand time zone
- Fixed HT503 did not detect incoming calls using PSTN from Telecom Italia
- Fixed HT503 NTT CID scheme did not work
- Fixed BJ Telcom Attended Transfer failure
- Fixed under "Enabled and forced" SRTP Mode, device cannot set up calls with IP Phone
- Fixed GXW400x RTP port is random on outgoing calls when hunting group is enabled
- Fixed TX audio from device is distorted
- Fixed when using inexpensive analog phones with our devices, sometimes there is slow ring problem, or no ringing at all. Updated RLX to -3dB for all SLICs. Added 20V DC offset to CHINA SLIC
- Fixed device did not send DNS request to "Preferred DNS server" under PPPoE
- Fixed HT503 FXO could not detect PSTN hang up
- Fixed HT503 FXO release time is too long
- Fixed XML Parser did not take multi-line P values in configuration file
- Fixed SIP TLS Private Key and certificate cannot be provisioned using XML. Added support of multi-line pvalues (279 and 280)

ENHANCEMENTS:

- Added busy tone when using Current Disconnect
- Added option to enable/disable Crypto life time when using SRTP