EX-4463 flr: ensure layout generation is incremented on merge

EX-4463 flr: ensure layout generation is incremented on merge

In lod_declare_layout_merge(), load the striping before we increment
the layout generation. Add sanity-flr:test_51a to check this.

Fixes: 6b5a29c0ac94 (Revert "LU-14642 flr: transfer layout version on layout change")
Test-Parameters: testlist=sanity-flr envdefinitions=FAIL_ON_ERROR=false,ONLY=51a,ONLY_REPEAT=20
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I357501edfd2bc0d710be902df9c40aab53c11824
Reviewed-on: https://review.whamcloud.com/46028
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>