sys/vm/uma_core.c:zone_import() Wrap stripe variable in #ifdef NUMA

[sbruno]

Summary

stripe seems to be unused on targets that don't support NUMA.
Wrap this variable completely inside of #ifdef NUMA. Found with gcc.

[sbruno]

/home/sbruno/bsd/fbsd_head/sys/vm/uma_core.c: In function 'zone_import':
/home/sbruno/bsd/fbsd_head/sys/vm/uma_core.c:2774:6: warning: variable 'stripe' set but not used [-Wunused-but-set-variable]
  int stripe;