One updateSummary method called by all VPN prefs

Having multiple methods means inevitably when new features are added to
the preferences, the right calls aren't made so information on the
screen lags between updates.

Bug: 28257641
Change-Id: I336aeefd5941ccf808dc9070427209a7d2530032
(cherry picked from commit 903843e6f9ead6f17d3685a551dc85083b147038)
3 files changed