libuweave: Fix break on Android toolchain

Android toolchain defines "unix" to be 1 which breaks one function
prototype in libuweave code. Changed the param name from "unix" to
"unix_timestamp".

Change-Id: Ic484d74aa3af1459af7cf6d15da4bc5b20226cf8
Reviewed-on: https://weave-review.googlesource.com/3120
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
diff --git a/third_party/libuweave/src/macaroon.h b/third_party/libuweave/src/macaroon.h
index 310f988..09c0459 100644
--- a/third_party/libuweave/src/macaroon.h
+++ b/third_party/libuweave/src/macaroon.h
@@ -110,8 +110,8 @@
 }
 
 /** Converts a unix timestamp to a j2000 timestamp. */
-static inline time_t uw_macaroon_unix_epoch_to_j2000(time_t unix) {
-  return unix - J2000_EPOCH_OFFSET;
+static inline time_t uw_macaroon_unix_epoch_to_j2000(time_t unix_timestamp) {
+  return unix_timestamp - J2000_EPOCH_OFFSET;
 }
 
 /**