[dhcp] Allow use of custom reallocation functions for DHCP option blocks

Allow functions other than realloc() to be used to reallocate DHCP
option block data, and specify the reallocation function at the time
of calling dhcpopt_init().

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/dhcppkt.c

@@ -267,7 +267,8 @@ void dhcppkt_init ( struct dhcp_packet *dhcppkt, struct dhcphdr *data,
 	ref_init ( &dhcppkt->refcnt, NULL );
 	dhcppkt->dhcphdr = data;
 	dhcpopt_init ( &dhcppkt->options, &dhcppkt->dhcphdr->options,
-		       ( len - offsetof ( struct dhcphdr, options ) ) );
+		       ( len - offsetof ( struct dhcphdr, options ) ),
+		       dhcpopt_no_realloc );
 	settings_init ( &dhcppkt->settings,
 			&dhcppkt_settings_operations, &dhcppkt->refcnt, 0 );
 }