Only allow the system server to connect to sync adapters

Bug: 203229608
Test: Manual test with changing the check logic + debug log
Change-Id: If18009f61360564d02dcda9b1e5fa15685e3250f
(cherry picked from commit 58270527d11ac7e5f07d337a402d8edf046a63ee)
(cherry picked from commit 7d1397a54475ed7fee632339ef7c60b432f0fbff)
Merged-In: If18009f61360564d02dcda9b1e5fa15685e3250f
1 file changed