Install parallel Child SAs using alias/subnets to get N parallel SAs.

RFC 7296 2.8
"IKEv2 deliberately allows parallel SAs with the same
Traffic Selectors between common endpoints."

NOTE: rightsubnet is repeated inside the rightsubnets.
rightsubnets=192.0.2.0/24,192.0.2.0/24

This test need kernel/xfrm support to distribute traffic over parallel SA.