send: Specify int as main()’s return type and include string.h

Fix the warnings below:

    $ make send
    cc     send.c   -o send
    send.c:41:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
     main(int argc,char *argv[]) {
     ^~~~
    send.c: In function ‘main’:
    send.c:63:5: warning: implicit declaration of function ‘memset’ [-Wimplicit-function-declaration]
         memset(buffer,0xA3,sizeof(buffer));
         ^~~~~~
    send.c:63:5: warning: incompatible implicit declaration of built-in function ‘memset’
    send.c:63:5: note: include ‘<string.h>’ or provide a declaration of ‘memset’
    send.c:79:5: warning: implicit declaration of function ‘memcpy’ [-Wimplicit-function-declaration]
         memcpy(&sin.sin_addr,he->h_addr,he->h_length);
         ^~~~~~
    send.c:79:5: warning: incompatible implicit declaration of built-in function ‘memcpy’
    send.c:79:5: note: include ‘<string.h>’ or provide a declaration of ‘memcpy’

Reported-by: gcc (GCC) 7.5.0

send/send.c

@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <netinet/in.h>
@@ -38,7 +39,7 @@ void setLinger(int s)
 static char buffer[8192];
 
 
-main(int argc,char *argv[]) {
+int main(int argc,char *argv[]) {
 
     char *host;
     short port;