Stop using unqualified {GET,PUT}_32BIT.

Those were a reasonable abbreviation when the code almost never had to
deal with little-endian numbers, but they've crept into enough places
now (e.g. the ECC formatting) that I think I'd now prefer that every
use of the integer read/write macros was clearly marked with its
endianness.

So all uses of GET_??BIT and PUT_??BIT are now qualified. The special
versions in x11fwd.c, which used variable endianness because so does
the X11 protocol, are suffixed _X11 to make that clear, and where that
pushed line lengths over 80 characters I've taken the opportunity to
name a local variable to remind me of what that extra parameter
actually does.

sesschan.c

@@ -660,7 +660,7 @@ static int sftp_chan_send(Channel *chan, bool is_stderr,
         struct sftp_packet *pkt, *reply;
 
         bufchain_fetch(&sess->subsys_input, lenbuf, 4);
-        pktlen = GET_32BIT(lenbuf);
+        pktlen = GET_32BIT_MSB_FIRST(lenbuf);
 
         if (bufchain_size(&sess->subsys_input) - 4 < pktlen)
             break;                     /* wait for more data */