net: kill lltable_drain

It has been #if 0'd in freebsd too. It is dead code. Remove it.

Signed-off-by: Asias He <asias@cloudius-systems.com>
net: kill arp_ifinit2

It is used in sys/netinet/ip_carp.c by CARP[1][2] protocol which we do not
support it now and have very little chance to support it in the future.

[1] http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/carp.html
[2] http://www.freebsd.org/cgi/man.cgi?query=carp&sektion=4&n=1

Signed-off-by: Asias He <asias@cloudius-systems.com>
net: Remove dead code in if.cc

This is backport from freebsd:

   commit 58f7b15da98d85f702ada8a45f4e1f50c97f5155
   Author: melifaro <melifaro@FreeBSD.org>
   Date:   Tue Jan 7 19:00:40 2014 +0000

       Remove dead code.

       Reported by:        Coverity
       Coverity CID:       1018057
       MFC after:  2 weeks

       Reviewed by:        bz

Signed-off-by: Asias He <asias@cloudius-systems.com>
net: Remove ifa_ref()/ifa_free(), which are atomic(9), from ip_output()

This is backport from freebsd:

   commit 2c50988dca8f1c498ada4b3c8c0c275a7c324622
   Author: glebius <glebius@FreeBSD.org>
   Date:   Tue Mar 4 19:49:41 2014 +0000

       Remove ifa_ref()/ifa_free(), which are atomic(9), from ip_output().

       The ifaddr is already referenced by the rtentry, and we are holding
       reference on the rtentry throughout the function execution.

       Sponsored by:       Netflix
       Sponsored by:       Nginx, Inc.

Signed-off-by: Asias He <asias@cloudius-systems.com>
net: Do not leak ifa in ip_output

This is backport from freebsd:

   commit ab0c56942296d702f3fb3e9418d3cde78711097b
   Author: glebius <glebius@FreeBSD.org>
   Date:   Wed Jul 9 07:48:05 2014 +0000

       In several cases in ip_output() we obtain reference on ifa. Do not
       leak it.

Signed-off-by: Asias He <asias@cloudius-systems.com>