xt_condition: remove `wmb` when adding new variable

xt_condition: remove `wmb` when adding new variable

Originally, some accesses to `conditions_list` were protected by RCU and
the memory-barrier was needed to ensure that the new variable was fully
initialized before being added to the list.  These days, however, all
accesses are protected by the `proc_lock` mutex, so the barrier is no
longer required.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>