wg-quick: freebsd: rebreak interface loopback, while fixing localhost

The commit 7c833642 ("wg-quick: freebsd: allow loopback to work") was
supposed to make things better, but actually it just started sending
legitimate localhost traffic over the WireGuard interface, which is
really quite bad.

This reverts commit 7c833642dfa342218602ab18e7091e86408d2982.

Reported-by: Matt Smith <matt.xtaz@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/wg-quick/freebsd.bash

@@ -158,7 +158,7 @@ add_addr() {
 	if [[ $1 == *:* ]]; then
 		cmd ifconfig "$INTERFACE" inet6 "$1" alias
 	else
-		cmd ifconfig "$INTERFACE" inet "$1" 127.0.0.1 alias
+		cmd ifconfig "$INTERFACE" inet "$1" "${1%%/*}" alias
 	fi
 }