Add MdnsPacketRepeater

MdnsPacketRepeater is a base class to send packets at various intervals.

It will be used to implement probing or advertising, which involves
sending a packet multiple times.

Bug: 241738458
Test: atest MdnsAnnouncerTest (with MdnsAnnouncer change)
Change-Id: I4febbc3eb5472701cb7999b6dba6259246ff46ee
5 files changed