secchan: Fix use-after-free by allocating rule actions as separate blocks.

secchan: Fix use-after-free by allocating rule actions as separate blocks.

The ofproto code tried to cleverly save memory and time by allocating
rule actions as a flexible array member at the end of "struct rule".  When
the actions changed, this required a realloc() call.  Unfortunately, there
are sometimes pointers to rules (e.g. the "super" pointer from subrules)
that were not getting adjusted to point to the new location.

It's better to just allocate actions separately, so fix it by doing that.