Remove residual blank line at start of Makefile

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

tcp: fix build issue for some cc modules

The TCP_HHOOK option was moved from opt_inet.h to opt_global.h in
https://cgit.FreeBSD.org/src/commit/?id=e68b3792440cac248347afe08ba5881a00ba6523
The corres

tcp: fix build issue for some cc modules

The TCP_HHOOK option was moved from opt_inet.h to opt_global.h in
https://cgit.FreeBSD.org/src/commit/?id=e68b3792440cac248347afe08ba5881a00ba6523
The corresponding changes in two Makefiles were missed, which resulted
in not building cc_cdg, cc_chd, cc_hd, and cc_vegas anymore.

Reported by: void@f-m.fm
Reviewed by: rrs, rscheff
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D41010

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Merge ^/head r306906 through r307382.

In the TCP stack, the hhook(9) framework provides hooks for kernel modules
to add actions that run when a TCP frame is sent or received on a TCP
session in the ESTABLISHED state. In the base tree, th

In the TCP stack, the hhook(9) framework provides hooks for kernel modules
to add actions that run when a TCP frame is sent or received on a TCP
session in the ESTABLISHED state. In the base tree, this functionality is
only used for the h_ertt module, which is used by the cc_cdg, cc_chd, cc_hd,
and cc_vegas congestion control modules.

Presently, we incur overhead to check for hooks each time a TCP frame is
sent or received on an ESTABLISHED TCP session.

This change adds a new compile-time option (TCP_HHOOK) to determine whether
to include the hhook(9) framework for TCP. To retain backwards
compatibility, I added the TCP_HHOOK option to every configuration file that
already defined "options INET". (Therefore, this patch introduces no
functional change. In order to see a functional difference, you need to
compile a custom kernel without the TCP_HHOOK option.) This change will
allow users to easily exclude this functionality from their kernel, should
they wish to do so.

Note that any users who use a custom kernel configuration and use one of the
congestion control modules listed above will need to add the TCP_HHOOK
option to their kernel configuration.

Reviewed by: rrs, lstewart, hiren (previous version), sjg (makefiles only)
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D8185

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Merge svn+ssh://svn.freebsd.org/base/head@218816

Import the ERTT (Enhanced Round Trip Time) Khelp module. ERTT uses the
Khelp/Hhook KPIs to hook into the TCP stack and maintain a per-connection, low
noise estimate of the instantaneous RTT. ERTT's i

Import the ERTT (Enhanced Round Trip Time) Khelp module. ERTT uses the
Khelp/Hhook KPIs to hook into the TCP stack and maintain a per-connection, low
noise estimate of the instantaneous RTT. ERTT's implementation is robust even in
the face of delayed acknowledgements and/or TSO being in use for a connection.

A high quality, low noise RTT estimate is a requirement for applications such as
delay-based congestion control, for which we will be importing some algorithm
implementations shortly.

In collaboration with: David Hayes <dahayes at swin edu au> and
Grenville Armitage <garmitage at swin edu au>
Sponsored by: FreeBSD Foundation
Reviewed by: bz and others along the way
MFC after: 3 months

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Add build infrastructure for Khelp modules.

Sponsored by: FreeBSD Foundation
Reviewed by: bz
MFC after: 3 months