LU-11691 lov: Limit layout size to max ea size

LU-11691 lov: Limit layout size to max ea size

The layout code does not currently prevent the creation of
layouts which (once instantiated) will exceed the maximum
xattr size.

This patch modifies the code which calculates the maximum
allowed stripe count for a component to also evaluate the
full size of new layouts and report a count of zero if the
new layout is too large.  The server will then return
 -E2BIG to the client asking for such a layout.

Unfortunately, it's not practical to test this without
overstriping.  LU-9846 adds tests for this.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I2ead7702780b2600cf09485e06393ee9bcfb4a1e
Reviewed-on: https://review.whamcloud.com/34171
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>