LU-14291 ptlrpc: format UPDATE messages in server-only code

LU-14291 ptlrpc: format UPDATE messages in server-only code

There are some ptlrpc messages that are only used for targets to
communicate with each other: Object Updates between Targets (OUT).

These are never needed by the client, so the code for handling them
can be conditionally compiled with HAVE_SERVER_SUPPORT.

The code in layout.c needs struct declaration that are in the file, so
group them at the end of the file and add #ifdef.
The code in pack_generic.c can stand alone, so move it to a new
pack_server.c and compile that only when server code is requested.

For simplicity, also make req_check_sepol() completely server-side
and provide an inline stub for client-only code.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I788352575a2109df389760fff45207ad6de3391b
Reviewed-on: https://review.whamcloud.com/41125
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>