Fix ro.telephony.default_network setting parsing

* The code that parses ro.telephony.default_network is broken,
instead of reading numbers separate by comma, it reads the first
number and replicates it for other slots. Settings like "8,1" will
be written to the db as "8,8"

Change-Id: I6b77000e00ada02ec89b09c752a9b337a6a8182b
(cherry picked from commit 746dc496)