In vfs_write_suspend_umnt(), if suspension cannot be established, do
not forget to restore write ops count when returning the error.

Reported and tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Fix mdoc warning.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Add OBJDUMP to sys.mk. The EFI loader uses it however without this it can
be set but empty.

Obtained from:	ABT Systems
Sponsored by:	The FreeBSD Foundation
Merge from projects/sendfile:
  Use sbcut_locked() instead of manually editing a sockbuf.

Sponsored by:	Nginx, Inc.
- Use NULL to compare a pointer.
- Use KASSERT() instead of panic.
- Remove useless 'continue', no need to restart cycle here.

Sponsored by:	Nginx, Inc.