storaged: protect global proto_loaded

proto_loaded is not thread safe, so we must protect it with
a mutex proto_lock.

Signed-off-by:  <hanhongli@360.cn>
Signed-off-by:  <gongguang@360.cn>
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 170732441
Test: compile
Change-Id: I93416598b6047e890c66b922b360093aa42db8c5
(cherry picked from commit 33206d39)