Merge projects/ipsec into head/.

Small summary

o Almost all IPsec releated code was moved into sys/netipsec.
o New kernel modules added: ipsec.ko and tcpmd5.ko. New kernel

option IPSEC_SUPPORT added. It enables support for loading
and unloading of ipsec.ko and tcpmd5.ko kernel modules.

o IPSEC_NAT_T option was removed. Now NAT-T support is enabled by

default. The UDP_ENCAP_ESPINUDP_NON_IKE encapsulation type
support was removed. Added TCP/UDP checksum handling for
inbound packets that were decapsulated by transport mode SAs.
setkey(8) modified to show run-time NAT-T configuration of SA.

o New network pseudo interface if_ipsec(4) added. For now it is

build as part of ipsec.ko module (or with IPSEC kernel).
It implements IPsec virtual tunnels to create route-based VPNs.

o The network stack now invokes IPsec functions using special

methods. The only one header file <netipsec/ipsec_support.h>
should be included to declare all the needed things to work
with IPsec.

o All IPsec protocols handlers (ESP/AH/IPCOMP protosw) were removed.

Now these protocols are handled directly via IPsec methods.

o TCP_SIGNATURE support was reworked to be more close to RFC.
o PF_KEY SADB was reworked:

• now all security associations stored in the single SPI namespace, and all SAs MUST have unique SPI.
• several hash tables added to speed up lookups in SADB.
• SADB now uses rmlock to protect access, and concurrent threads can do SA lookups in the same time.
• many PF_KEY message handlers were reworked to reflect changes in SADB.
• SADB_UPDATE message was extended to support new PF_KEY headers: SADB_X_EXT_NEW_ADDRESS_SRC and SADB_X_EXT_NEW_ADDRESS_DST. They can be used by IKE daemon to change SA addresses.

o ipsecrequest and secpolicy structures were cardinally changed to

avoid locking protection for ipsecrequest. Now we support
only limited number (4) of bundled SAs, but they are supported
for both INET and INET6.

o INPCB security policy cache was introduced. Each PCB now caches

used security policies to avoid SP lookup for each packet.

o For inbound security policies added the mode, when the kernel does

check for full history of applied IPsec transforms.

o References counting rules for security policies and security

associations were changed. The proper SA locking added into xform
code.

o xform code was also changed. Now it is possible to unregister xforms.

tdb_xxx structures were changed and renamed to reflect changes in
SADB/SPDB, and changed rules for locking and refcounting.

Reviewed by: gnn, wblock
Obtained from: Yandex LLC
Relnotes: yes
Sponsored by: Yandex LLC
Differential Revision: https://reviews.freebsd.org/D9352