libnetutils: add ifc_set_mtu

Change-Id: I3031e9ee38583648350f2c46baa7a9a714b9ea1e
adb: Add "wait-for-sideload" command

 * Waits for connected device to enter sideload mode

Change-Id: I65b4ad86456c13a3bbc48880e12ab7a034707b88