BUG/MINOR: log: fix potential lf->name memory leak

BUG/MINOR: log: fix potential lf->name memory leak

Recent commit 2ed6068 ("MINOR: log: custom name for logformat node")
introduced a potential memory leak because when custom name is provided,
lf->name value is allocated using strdup(), thus is expected to be freed
alongside the node when the node is released.

However lf->name was only freed in some common places within log.c
cleanups and helpers func, but in reality there are still cases where
lf nodes are manually freed without making use of freeing helpers.

So this is what this patch does, it makes sure all lf freeing places now
leverage the free_logformat_node() helper function that takes care of
freeing all known allocated elements within the node, including custom
name.

This commit depends on:
 - "MINOR: log: add free_logformat_node() helper function"

No backport needed unless 2ed6068 gets backported.