Remove unreachable break in zfs_main.c
Partial import of illumos changeset 13622:e5889df1eaac
2077 lots of unreachable breaks in illumos gate
References:
https://www.illumos.org/issues/2077
PR: kern/167370
Submitted by: Marcelo Araujo <araujo@FreeBSD.org>
Obtained from: illumos (issue #2077)
MFC after: 1 week