child-sa: Fix refcounting of allocated reqids

child-sa: Fix refcounting of allocated reqids

During a rekeying we want to reuse the current reqid, but if the new SA
does not allocate it via kernel-interface the state there will disappear
when the old SA is destroyed after the rekeying.  When the IKE_SA is
later reauthenticated with make-before-break reauthentication the new
CHILD_SAs there will get new reqids as no existing state is found in the
kernel-interface, breaking policy installation in the kernel.

Fixes: a49393954f31 ("child-sa: Use any fixed reqid configured on the CHILD_SA config")