Use unsuspend_all_lwps

This patch is to replace find_inferior (&all_threads, unsuspend_one_lwp, NULL)
with unsuspend_all_lwps (NULL), which is shorter.  They are equivalent
to each other.

gdb/gdbserver:

2016-05-17  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (linux_stabilize_threads): Call unsuspend_all_lwps
	instead of find_inferior.