Close idle connections to release RAM

Close idle connections after 30s of inactivity to release RAM.
Savings: ~1MB on marlin, 0.5MB on low-ram devices

Bug: 63398887
Test: reboot and dumpsys meminfo com.android.phone
Change-Id: I38256e224ee090f1be0e26b2c5e8451743ca8c96
3 files changed