tree-wide: when %m is used in log_*, always specify errno explicitly

All those uses were correct, but I think it's better to be explicit.
Using implicit errno is too error prone, and with this change we can require
(in the sense of a style guideline) that the code is always specified.

Helpful query: git grep -n -P 'log_[^s][a-z]+\(.*%m'

src/stdio-bridge/stdio-bridge.c

@@ -292,7 +292,7 @@ int main(int argc, char *argv[]) {
                         r = ppoll(p, ELEMENTSOF(p), ts, NULL);
                 }
                 if (r < 0) {
-                        log_error("ppoll() failed: %m");
+                        log_error_errno(errno, "ppoll() failed: %m");
                         goto finish;
                 }
         }