ANDROID: make sure proc mount options are applied

Android relies on the "hidepid" mount option for /proc on
the 2nd mount, however the upstream kernel requires options
on the first mount and ignores options afterwards.

In prevous Android kernels, this was fixed by reverting
upstream commit e94591d0 ("proc: Convert proc_mount
to use mount_ns."). The upstream code has now been
refactored to the point that a new fix is needed. This
patch applies mount options during proc_get_tree() to
ensure the most recently parsed options are applied.

Bug: 145626724
Test: atest CtsOsTestCases:android.os.cts.EnvironmentTest#testHidePid2
Change-Id: I3d402f98e826e2f03ad366da7d05b3eeaaa90c26
Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Matthias Maennich <maennich@google.com>