Refresh security pref in Network Details page

Security type of WifiEntry may change based on available
scans/configs/the current connection for entries that can support
multiple security types. Refresh the security string every time the
WifiEntry is updated.

Bug: 185914718
Test: manual inspection that connected wifi entry has the correct
security string

Change-Id: I5f3b7274f1e6b68de414493a6619555ee9b17e23