qmail-smtpd: introduce an array of EHLO string generators

This is of no direct use for the vanilla version, but it allows to simplify
the integration of different patches which add add EHLO arguments. They will
only need to add their print function to this array and it will get called.

qmail-smtpd.c

@@ -60,6 +60,9 @@ void err_noop(arg) char *arg; { out("250 ok\r\n"); }
 void err_vrfy(arg) char *arg; { out("252 send some mail, i'll try my best\r\n"); }
 void err_qqt() { out("451 qqt failure (#4.3.0)\r\n"); }
 
+static void (*ehlo_gen[])() = {
+	NULL
+};
 
 stralloc greeting = {0};
 
@@ -230,7 +233,12 @@ void smtp_helo(arg) char *arg;
 }
 void smtp_ehlo(arg) char *arg;
 {
-  smtp_greet("250-"); out("\r\n250-PIPELINING\r\n250 8BITMIME\r\n");
+  unsigned int i;
+  smtp_greet("250-");
+  for (i = 0; ehlo_gen[i]; i++) {
+    ehlo_gen[i]();
+  }
+  out("\r\n250-PIPELINING\r\n250 8BITMIME\r\n");
   seenmail = 0; dohelo(arg);
 }
 void smtp_rset(arg) char *arg;