utils: Add ast_assert_return

utils:  Add ast_assert_return

Similar to pjproject's PJ_ASSERT_RETURN macro, this one will do the
following...

If the assert passes... NoOp

If the assert fails and AST_DEVMODE is defined, execute ast_assert()
then, if DO_CRASH isn't set, return from the calling function with
the supplied value.

If the assert fails and AST_DEVMODE is not defined, return from the
calling function with the supplied value.

The macro will execute a return without a value if one isn't suppled.

Change-Id: I0003844affeab550d5ff5bca7aa7cf8a559b873e