Don't use a manually-sized buffer for the PID.

Change-Id: Ibdda590b828c61caa488e959f3e596dc981a2c65
diff --git a/server/NetdConstants.h b/server/NetdConstants.h
index 5c3fde0..686e974 100644
--- a/server/NetdConstants.h
+++ b/server/NetdConstants.h
@@ -44,6 +44,7 @@
 
 #define __INT_STRLEN(i) sizeof(#i)
 #define _INT_STRLEN(i) __INT_STRLEN(i)
+#define INT32_STRLEN _INT_STRLEN(INT32_MIN)
 #define UINT32_STRLEN _INT_STRLEN(UINT32_MAX)
 #define UINT32_HEX_STRLEN sizeof("0x12345678")