[CLATJ#5] libclat: move detect_mtu() from netd to apex

detect_mtu() is moved from ClatdController without behavior
change. The unique_fd for socket fd is replaced by primitive int
because libbase is not supported in mainline.

Bug: 212345928
Test: build and boot
      atest libclat_test
Change-Id: Ib9c1a9d4b9e1c141d88164e8489c5044fdf70685
diff --git a/service/native/libs/libclat/Android.bp b/service/native/libs/libclat/Android.bp
index a45ffa6..9fe441a 100644
--- a/service/native/libs/libclat/Android.bp
+++ b/service/native/libs/libclat/Android.bp
@@ -22,6 +22,7 @@
     srcs: ["clatutils.cpp"],
     stl: "libc++_static",
     static_libs: ["libip_checksum"],
+    shared_libs: ["liblog"],
     export_include_dirs: ["include"],
     min_sdk_version: "30",
     apex_available: ["com.android.tethering"],
@@ -39,4 +40,5 @@
         "libclat",
         "libip_checksum",
     ],
+    shared_libs: ["liblog"],
 }
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