LU-12316 llog: convert llog_client defines to functions

LU-12316 llog: convert llog_client defines to functions

Convert preprocessor functions into actual functions. The
original commit that added these macros (81c713adeb) did
not provide an explaination for why these were chosen to
be macros rather than functions. Hence, bias towards using
functions rather than complex macros since they appear
in stack traces, are easier to debug, and simpler to
develop with.

Signed-off-by: Ben Evans <bevans@cray.com>
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I7a73e9af57dcf5edb9d013272ff5cf85e4234146
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/34904
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>