ntpd: commonalize message strings

ntpd: commonalize message strings

function                                             old     new   delta
recv_and_process_peer_pkt                            961     973     +12
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/0 up/down: 12/0)               Total: 12 bytes
   text	   data	    bss	    dec	    hex	filename
 953108	    481	   7288	 960877	  ea96d	busybox_old
 953086	    481	   7288	 960855	  ea957	busybox_unstripped

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