httpd: require "HTTP/xyz" at the end of request line

httpd: require "HTTP/xyz" at the end of request line

function                                             old     new   delta
handle_incoming_and_exit                            2379    2362     -17
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-17)             Total: -17 bytes
   text	   data	    bss	    dec	    hex	filename
 981787	    485	   7296	 989568	  f1980	busybox_old
 981779	    485	   7296	 989560	  f1978	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>