Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: I226a0599db4f7c3557e55cade7869d00bd314949
diff --git a/client/NetdClient.cpp b/client/NetdClient.cpp
index a46dc93..3fd985e 100644
--- a/client/NetdClient.cpp
+++ b/client/NetdClient.cpp
@@ -42,9 +42,9 @@
 
 // These variables are only modified at startup (when libc.so is loaded) and never afterwards, so
 // it's okay that they are read later at runtime without a lock.
-Accept4FunctionType libcAccept4 = 0;
-ConnectFunctionType libcConnect = 0;
-SocketFunctionType libcSocket = 0;
+Accept4FunctionType libcAccept4 = nullptr;
+ConnectFunctionType libcConnect = nullptr;
+SocketFunctionType libcSocket = nullptr;
 
 int closeFdAndSetErrno(int fd, int error) {
     close(fd);