rcu: just rename call_rcu_bh instead of making it a macro

Seems that I found a box that has a config that passes call_rcu_bh as a
function pointer (see net/sctp/sm_make_chunk.c), so declaring the
call_rcu_bh has a macro function isn't good enough.

This patch makes it just another name of call_rcu for rcupreempt.

Signed-off-by: Steven Rostedt <srostedt@redhat.org>
Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>