Change BUG_ON and WARN_ON to give the compiler a chance to perform
compile-time optimsations. Depending on the complexity of the condition,
the compiler may not do this very well, so if it's important check the
object code.

Current GCC's (4.x) produce good code as long as the condition does not
include a function call, including a static inline.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>