utils.py: Add helper method to encode ePDGSelection info TLV

Encodes ePDGSelection info TLV so it can be stored at EF.ePDGSelection or EF.ePDGSelectionEm.
See 3GPP TS 31.102 version 15.2.0 Release 15, section 4.2.104 and 4.2.106.

Take original hex string of EF.ePDGSelection or EF.ePDGSelectionEm, MCC,
MNC, ePDG priority for PLMN and ePDG FQDN Format to use for PLMNas input
and outputs the encoded hex string.

Change-Id: Ia7292d33783c770a3bb91b081c671af36bbb907f

pySim/utils.py

@@ -610,6 +610,22 @@ def init_reader(opts):
 
 	return sl
 
+def enc_ePDGSelection(hexstr, mcc, mnc, epdg_priority='0001', epdg_fqdn_format='00'):
+	"""
+	Encode ePDGSelection so it can be stored at EF.ePDGSelection or EF.ePDGSelectionEm.
+	See 3GPP TS 31.102 version 15.2.0 Release 15, section 4.2.104 and 4.2.106.
+
+	Default values:
+		- epdg_priority: '0001' - 1st Priority
+		- epdg_fqdn_format: '00' - Operator Identifier FQDN
+	"""
+
+	plmn1 = enc_plmn(mcc, mnc) + epdg_priority + epdg_fqdn_format
+	# TODO: Handle encoding of Length field for length more than 127 Bytes
+	content = '80' + ('%02x' % (len(plmn1)//2)) + plmn1
+	content = rpad(content, len(hexstr))
+	return content
+
 def dec_ePDGSelection(sixhexbytes):
 	"""
 	Decode ePDGSelection to get EF.ePDGSelection or EF.ePDGSelectionEm.