kern/53848: ipsecif_{basic,ioctl}_ipv6overipv6_esp_* test cases fail randomly

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         53848
>Category:       kern
>Synopsis:       ipsecif_{basic,ioctl}_ipv6overipv6_esp_* test cases fail randomly
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jan 09 15:45:00 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

Four test cases of the net/if_ipsec/t_ipsec test, all involving
"ipv6overipv6_esp", are failing randomly.  They don't fail very often
on the qemu-based testbeds, but each one fails in about a third of the
runs on real hardware (tested on an 8-core HP DL360 G7).  Here is a
summary of the outcomes from my last 30 test runs, with each failure
marked by "X" and each success by "-":

---X---X--X-X---XX----XX--XXX--X--------   net/if_ipsec/t_ipsec:ipsecif_basic_ipv6overipv6_esp_null
X---X--------X-X---XX-XX-XX--------X---X   net/if_ipsec/t_ipsec:ipsecif_basic_ipv6overipv6_esp_rijndaelcbc
X------XX-----XX----------------X-----X-   net/if_ipsec/t_ipsec:ipsecif_ioctl_ipv6overipv6_esp_null
--X-----------X---X---------XXX-X-X---X-   net/if_ipsec/t_ipsec:ipsecif_ioctl_ipv6overipv6_esp_rijndaelcbc

The first failures were logged the day after the test was renamed to
its present name soon after being committed in January 2018, so it
seems likely that the problem has existed for at least as long as the
test.

Log output from the latest failure on my testbed is at:

  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.01.09.10.51.23/test.html#net_if_ipsec_t_ipsec_ipsecif_basic_ipv6overipv6_esp_rijndaelcbc

>How-To-Repeat:

Run the ATF tests repatedly on real hardware.

>Fix: