Refactor tap/bridge/dnsmasq create/destroy
Refactor tap/bridge/dnsmasq create/destroy

Allows future changes to the wifi bridges to be implemented with less
code duplication.

Signed-off-by: Alistair Delva <23ee790dfac9f550e53930edf0f667e54338af85@google.com>

google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish