Try to more safely handle empty hostnames.

Test: as follows
    - built
    - flashed
    - booted
    - manual testing in modes: {off, opportunistic, strict}
    - system/netd/tests/runtests.sh
Bug: 74606156
Merged-In: I0f887be19affcf54f7ab3d90cf7c4ecc08e4f93f
Merged-In: Iffe4434ac7438da4407e80a8714462a3e4a8e262
Change-Id: I183e5de0ba77571fefd686ac0a9e53e6011722a4
(cherry picked from commit 8541c21a)