- When reconfiguring protocol on a lagg, first set it to LAGG_PROTO_NONE,
  then drop lock, run the attach routines, and then set it to specific
  proto. This removes tons of WITNESS warnings.
- Make lagg protocol attach handlers not failing and allocate memory
  with M_WAITOK.

Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272161 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f