MFC r310180, r310327

MFC r310180, r310327

r310180:
Fix panic during lagg destruction with simultaneous status check

If you run "ifconfig lagg0 destroy" and "ifconfig lagg0" at the same time a
page fault may result. The first process will destroy ifp->if_lagg in
lagg_clone_destroy (called by if_clone_destroy). Then the second process
will observe that ifp->if_lagg is NULL at the top of lagg_port_ioctl and
goto fallback: where it will promptly dereference ifp->if_lagg anyway.

The solution is to repeat the NULL check for ifp->if_lagg

MFC after:	4 weeks
Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D8512

r310327:
Remove stray debugging code from r310180

Reported by:	rstone
Pointy hat to:	asomers
MFC after:	3 weeks
X-MFC-with:	310180
Sponsored by:	Spectra Logic Corp

git-svn-id: svn://svn.freebsd.org/base/stable/10@313112 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f