LU-13055 mdd: don't assert on unknown changelog lrh_type

LU-13055 mdd: don't assert on unknown changelog lrh_type

Supplemental patch for old server code to prevent assertion
on unknown/new changelog record and user record types

Test-Parameters: env=ONLY=160 testlist=sanity serverjob=lustre-master serverbuildno=0
Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I5d45c6ef659feb2b143edf6286df9904378171ba
Reviewed-on: https://review.whamcloud.com/43710
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>