Extend tethering enable/disable timeout to 30 seconds

The dnsmasq in R might block netd for 20 seconds, which can also
block tethering enable/disable for 20 seconds. To fix this, changing
the timeouts from 5 seconds to 30

Bug: 289881008
Test: TH
Change-Id: Ibed5895b2831465d454854d7250fcc44183596e2