Fix clang-tidy warnings in log_time.h

 - Zero initialize log_time instances by default
 - Disable implicit conversions by making constructors explicit
 - Explicitly initialize to EPOCH in most places
 - Change sniffTime() to avoid in-place modification of a log_time

I stopped here, but we could consider following up with a more invasive
change to make log_time instances immutable and perhaps also remove the
default constructor to force explicit initialization to EPOCH.

Test: atest libbase_test netd_unit_test
Change-Id: I67e716ef74adaaf40ab2c6e2e0dddb8d309bc7ca
diff --git a/logd/LogBuffer.cpp b/logd/LogBuffer.cpp
index fbdbf79..9cbc7c4 100644
--- a/logd/LogBuffer.cpp
+++ b/logd/LogBuffer.cpp
@@ -399,7 +399,7 @@
                         ((*it)->getLogId() != LOG_ID_KERNEL))) {
         mLogElements.push_back(elem);
     } else {
-        log_time end = log_time::EPOCH;
+        log_time end(log_time::EPOCH);
         bool end_set = false;
         bool end_always = false;