Allow starting dnsmasq without DHCP

dnsmasq will not start DHCP if no --dhcp-range flag is set. Allow
tethering start command to be called without DHCP ranges, so dnsmasq can
be started without this flag.

Bug: b/109584964
Test: manual: flashed a build with no --dhcp-range flag

Change-Id: I109f64240690aef701deabd49120eab0aba0e8a8
2 files changed