Ensure MTU is set for new interfaces.

Setting the MTU for an interface should not be skipped when the
interface names are different. This occurs when a VPN network creates
a new interface with identical MTU.

Bug: 246398088
Test: atest ConnectivityServiceTest
Test: Manual test: Connect to VPN network and switch networks
Test: Confirm MTU of interface is set correctly with `adb shell ip addr`
Change-Id: I811a01feca2fb2130c57c6c924145314180434c5
2 files changed