[PATCH]: some optimizations related to vrele + stuff

hi

there are places with mtx_lock(&Giant);vrele(...);mtx_unlock(&Giant); which is
unecessary + some other Giant usages which is not (imho) needed

its kern/86290 or the patch hysteria.sk/~neologism/kern.patch, pls test and
possibly (if correct) commit

thnx

roman