<unistd.h>: Fix profil(2) prototype.

<unistd.h>: Fix profil(2) prototype.

 First off the vm_offset_t is somewhat bogus in this context, same could
 be said about size_t variant in sys/sysproto.h.  Just use plain u_long
 type like it is already used in "struct uprof" and fix forth argument
 to take u_int.  In public headers prefer to use generic types.