Set min_sdk_version: 29

to ensure that libnetd_resolv is built against stubs of version 29.

Bug: 145796956
Test: m
      look into build.ninja to see if libnetd_resolv is built against
      stubs of version 29 for libc/libdl/libm.
Change-Id: I547d4fde4e0a32d3c49c9e3d4f9c4bc6ec4165b2