Fix:
IP Filter bug 1835705: It is impossible to delete a state using
SIOCDELST ioctl.

This is a direct commit to the stable/9 branch because this patch was
already included in the ipfilter 5.1.2 import in r254562. It was
ultimately included in ipfilter 4.1.29 (whereas stable/9 uses 4.1.28).

Obtained from: ipfilter CVS repo: ip_state.c r1.13