Re-purpose helper method to be used for parsing Address TLV Object in general

The Address TLV object is used in EF.P-CSCF Address, EF.ePDGId and EF.ePDGIdEm.
See 3GPP TS 31.102 version 13.4.0 Release 13, section 4.2.8, 4.2.102 and 4.2.104.

Address TLV Object format
Tag (1 Byte) - '80'
Length (1 Byte)
Address Type (1 Byte) - '00' (FQDN), '01' (IPv4), '02' (IPv6)
Address (Address Length Bytes)

Change-Id: Ifd8a240f6b5c7736e58a8151295c30ec5b32ed5f
diff --git a/pySim/cards.py b/pySim/cards.py
index 1036717..1662fc5 100644
--- a/pySim/cards.py
+++ b/pySim/cards.py
@@ -267,12 +267,12 @@
 	def read_epdgid(self):
 		(res, sw) = self._scc.read_binary(EF_USIM_ADF_map['ePDGId'])
 		if sw == '9000':
-			return (dec_epdgid(res), sw)
+			return (dec_addr_tlv(res), sw)
 		else:
 			return (None, sw)
 
 	def update_epdgid(self, epdgid):
-		epdgid_tlv = enc_epdgid(epdgid)
+		epdgid_tlv = enc_addr_tlv(epdgid)
 		data, sw = self._scc.update_binary(
 						EF_USIM_ADF_map['ePDGId'], epdgid_tlv)
 		return sw