MFC r257985:
  Fix panic with RADIX_MPATH, when RTFREE_LOCKED() called for already
  unlocked route. Use in6_rtalloc() instead of in6_rtalloc1. This helps
  simplify the code and remove several now unused variables.

  PR:		156283
Fix ABI broken in r270576. This is direct commit to stable/10.

Reported by:	kib