FreeBSD: convert teardown inactive lock to a read-mostly sleepable lock

The lock is taken all the time and as a regular read-write lock
avoidably serves as a mount point-wide contention point.

This forward ports FreeBSD revision r357322.

To quote aforementioned commit:

Sample result doing an incremental -j 40 build:
before: 173.30s user 458.97s system 2595% cpu 24.358 total
after:  168.58s user 254.92s system 2211% cpu 19.147 total

Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Signed-off-by: Mateusz Guzik <[email protected]>
Closes #10896 

0 files changed, 0 insertions, 0 deletions