contrib/check-config.sh: fix INET_XFRM_MODE_TRANSPORT
contrib/check-config.sh: fix INET_XFRM_MODE_TRANSPORT

This parameter was removed by kernel commit 4c145dce260137,
which made its way to kernel v5.3-rc1. Since that commit,
the functionality is built-in (i.e. it is available as long
as CONFIG_XFRM is on).

Make the check conditional.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

jthelin/docker,paralin/docker,mahak/docker,trebonian/docker,AkihiroSuda/docker,vdemeester/docker,jthelin/docker,thaJeztah/docker,thaJeztah/docker,paralin/docker,trebonian/docker,trebonian/docker,yosifkit/docker,flavio/docker,gnailuy/docker,nalind/docker,flavio/docker,cpuguy83/docker,trebonian/docker,moul/docker,vdemeester/docker,moul/docker,docker/docker,thaJeztah/docker,moul/docker,Mokolea/docker,moul/docker,djs55/docker,Ramzec/docker,Mokolea/docker,nalind/docker,kojiromike/docker,moby/moby,nawawi/docker,AkihiroSuda/docker,thaJeztah/docker,Ramzec/docker,kojiromike/docker,nawawi/docker,gnailuy/docker,cpuguy83/docker,konstruktoid/docker-upstream,cpuguy83/docker,Mokolea/docker,paralin/docker,djs55/docker,moby/moby,mahak/docker,jameszhan/docker,nawawi/docker,bearstech/moby,AkihiroSuda/docker,konstruktoid/docker-upstream,moby/moby,jimjag/docker,jimjag/docker,moby/moby,nalind/docker,Mokolea/docker,gnailuy/docker,AkihiroSuda/docker,bearstech/moby,docker/docker,nawawi/docker,jameszhan/docker,yosifkit/docker,Ramzec/docker,gnailuy/docker,jameszhan/docker,flavio/docker,flavio/docker,bearstech/moby,docker/docker,jimjag/docker,kojiromike/docker,mahak/docker,djs55/docker,konstruktoid/docker-upstream,cpuguy83/docker,yosifkit/docker,Ramzec/docker,bearstech/moby,jimjag/docker,mahak/docker,yosifkit/docker,vdemeester/docker,paralin/docker,nalind/docker,konstruktoid/docker-upstream