Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: I5b4123bc6709641315120a191e36cc57541349b2
diff --git a/libc/bionic/recv.cpp b/libc/bionic/recv.cpp
index 60f264d..32a7a72 100644
--- a/libc/bionic/recv.cpp
+++ b/libc/bionic/recv.cpp
@@ -29,5 +29,5 @@
 #include <sys/socket.h>
 
 ssize_t recv(int socket, void *buf, size_t len, int flags) {
-  return recvfrom(socket, buf, len, flags, NULL, 0);
+  return recvfrom(socket, buf, len, flags, nullptr, nullptr);
 }