ipa: Fix the compilation of ipaccess-find on FreeBSD

FreeBSD does not offer the SO_BINDTODEVICE option. The closest
thing is the IP_RECVIF option and this is used here now.

openbsc/src/ipaccess/ipaccess-find.c

@@ -41,8 +41,13 @@ static int udp_sock(const char *ifname)
 		return fd;
 
 	if (ifname) {
+#ifdef __FreeBSD__
+		rc = setsockopt(fd, SOL_SOCKET, IP_RECVIF, ifname,
+				strlen(ifname));
+#else
 		rc = setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, ifname,
 				strlen(ifname));
+#endif
 		if (rc < 0)
 			goto err;
 	}