filedesc: plug 2 assignments to M_ZERO-ed pointers in falloc_noinstall

No functional changes.
Set the DROP_EN bit before the RX queue is brought up and active.

He noticed issues setting this bit in SRRCTL after the queue was up,
so doing it from the sysctl handler isn't enough and may not actually
work correctly.

This commit doesn't remove the sysctl path or try to change its
behaviour.  I'll talk with others about how to finish fixing that
before I tackle that.

PR:		kern/194311
Submitted by:	luigi
MFC after:	3 days
Sponsored by:	Norse Corp, Inc
Add a sysctl to allow disabling the monitoring thread.

Summary:
If a user uses powerd, or doesn't want to use the cycles monitoring, they can
now suspend the monitoring thread.

While here, reorganize the added prototypes to match existing groupings.

Reviewers: nwhitehorn, #powerpc, rpaulo

Reviewed By: #powerpc, rpaulo

Differential Revision: https://reviews.freebsd.org/D944
X-MFC-with:	r273009

MFC after:	3 weeks
Drop support for SSLv3.

MFC after:	1 week
Remove a build artifact of the USDT tests.

MFC after:	3 days