NFC: Switch CHECK_INTERFACE to be a more friendly macro statement.

In the process of upgrading to clang r349610, an improvement to the
-Wextra-semi diagnostic now catches redundant semicolons in code.
CHECK_INTERFACE is a macro statement (currently using an if with a code
block that ends in a '}'). Since most callers are treating this as a
pseudo-function call, they terminate the macro with a semicolon. This
triggers the diagnostic, as we now have "if (...) { ... };", where the
semicolon is unnecessary.

To remedy these kinds of situations, it is better to construct macro
statements that require a semicolon to terminate them. This patch uses a
do/while wrapped around the existing statement, which is a pretty common
pattern for macro statements.

Bug: http://b/122481018
Test: m checkbuild
Change-Id: Ic2efc662f70f6b311e5d4581fb8e0eeb12a361f9