dtrace: syscall entry/return probes.

dtrace: syscall entry/return probes.

Makes the sys call table writable, and replaces the function pointer
for select syscalls with the address of a wrapper function to enable
entry and return probe firing.

Fix for address range checking for copyin(str) operations and relatives.
It was using an incorrect boundary address, causing problems for some cases.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>