isMMapEnabled() always returns false if setMMapEnabled(f) never called

[philburk]

Oboe version: 1.8.1 and earlier
App name used for testing: OboeTester

Short description
Jiabin found an error in isMMapEnabled().
It returns a true if MMAP policy is set for MMAP on.
But if the policy is UNSPECIFIED then it returns false, even if MMAP is enabled in the system.

Steps to reproduce
I added logging to OboeTester and then ran this test before setMMapEnabled(f) was called.

• print isMMapSupported()
• print isMMapEnabled()

Expected behavior
If MMspSupported() then MMapEnabled() should also be true.

Actual behavior
isMMapEnabled() is false.

[philburk]

Tracked internally in b/326989822 | P1 | Use AAudioExtensions to get/set mmap policy enabled does not work as expected