Move DnsSdTxtRecord to net common static library

DnsSdTxtRecord is moved to frameworks/libs/net for mainline
support. Also change the import path using this class.

Bug: 139268426
Bug: 135998869
Test: atest FrameworksNetTests
      ./frameworks/opt/net/wifi/tests/wifitests/runtests.sh

Change-Id: I6118b313ce668707d598aa2eab9baee2f7622dbc
Merged-In: I6118b313ce668707d598aa2eab9baee2f7622dbc