Always call into native loader when loading a native library

Namespace semantic has been enabled at native bridge side. And,
native loader wraps both dynamic linker and native bridge. ART
on longer calls native bridge directly when it loads a native
library, but still remembers whether native bridge is needed
for each library.

Bug: http://b/28242460


Test: make -j4 test-art-target && make -j32 test-art-host
Change-Id: I5eae4b7d492d9a476343301506d7028ed2a18e90
Signed-off-by: Zhenhua WANG <zhenhua.wang@intel.com>