Suppress IpServer message logs

To avoid log flooding, suppress CMD_IPV6_TETHER_UPDATE and
CMD_NEIGHBOR_EVENT message log because they appear frequentlg and
don't have any content which means they are ueseless for debugging.
Also remove logMessage from BaseServingState to fix duplicated
message because all the message already log in TetheredState
and LocalHotspotState which inherit BaseServingState.

Bug: 162920185
Bug: 185649441
Test: atest TetheringCoverageTests
      atest MtsTetheringTestLatestSdk
      atest CtsTetheringTest
Change-Id: Ib8fe719f3c1c4a65e6b5152df5e5adf33aba2079
Merged-In: Ib8fe719f3c1c4a65e6b5152df5e5adf33aba2079
1 file changed