LU-12741 ptlrpc: do lu_env_refill for new request

Perform lu_env_refill() prior any new request handling.
That was done already in tgt_request_handle() and is moved
now to ptlrpc_main() to work for any handler as well,
e.g. ldlm_cancel_handler()

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: Ic5d8bfbd845f7e131849078c016f7e13b91d072f
Reviewed-on: https://review.whamcloud.com/36714
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>