Only set IPV6_USE_MIN_MTU on IPv6.

(cherry picked from commit 561b780b)
15 jobs for 553-socket-c-2171-unexpected-error-v9_12 in 8 minutes and 56 seconds (queued for 49 seconds)
Status Job ID Name Coverage
  Precheck
passed precheck:debian:sid:amd64 #78229
amd64 docker linux

00:00:19

 
  Build
passed build:centos:centos6:amd64 #78230
amd64 docker linux

00:02:57

passed build:centos:centos7:amd64 #78231
amd64 docker linux

00:03:06

passed build:debian:sid:amd64 #78232
amd64 docker linux

00:02:10

passed build:debian:sid:i386 #78233
i386 docker linux

00:02:12

 
  Test
passed docs:debian:sid:amd64 #78234
amd64 docker linux

00:00:49

passed install:debian:sid:amd64 #78243
amd64 docker linux

00:03:01

passed systemtest:centos:centos6:amd64 #78239
amd64 docker linux

00:05:05

passed systemtest:centos:centos7:amd64 #78240
amd64 docker linux

00:04:43

passed systemtest:debian:sid:amd64 #78241
amd64 docker linux

00:04:47

passed systemtest:debian:sid:i386 #78242
i386 docker linux

00:05:25

passed unittest:centos:centos6:amd64 #78235
amd64 docker linux

00:00:58

passed unittest:centos:centos7:amd64 #78236
amd64 docker linux

00:01:06

passed unittest:debian:sid:amd64 #78237
amd64 docker linux

00:00:52

passed unittest:debian:sid:i386 #78238
i386 docker linux

00:00:58