slirp: remove dead increments, spotted by clang

Value stored is never read.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
index 7851307..0a370f1 100644
--- a/slirp/tcp_subr.c
+++ b/slirp/tcp_subr.c
@@ -857,7 +857,7 @@
 				if (p == 7071)
 				   p = 0;
 				*(u_char *)bptr++ = (p >> 8) & 0xff;
-				*(u_char *)bptr++ = p & 0xff;
+                                *(u_char *)bptr = p & 0xff;
 				ra = 0;
 				return 1;   /* port redirected, we're done */
 				break;