Fix a panic when leaving MC group in a kernel with VIMAGE enabled.
in_leavegroup() is called from an asynchronous task, and
igmp_change_state() requires that curvnet is set by the caller.
- Allow ND6_IFF_AUTO_LINKLOCAL for IFT_BRIDGE.  An interface with IFT_BRIDGE
  is initialized with !ND6_IFF_AUTO_LINKLOCAL && !ND6_IFF_ACCEPT_RTADV
  regardless of net.inet6.ip6.accept_rtadv and net.inet6.ip6.auto_linklocal.
  To configure an autoconfigured link-local address (RFC 4862), the
  following rc.conf(5) configuration can be used:

   ifconfig_bridge0_ipv6="inet6 auto_linklocal"

- if_bridge(4) now removes IPv6 addresses on a member interface to be
  added when the parent interface or one of the existing member
  interfaces has an IPv6 address.  if_bridge(4) merges each link-local
  scope zone which the member interfaces form respectively, so it causes
  address scope violation.  Removal of the IPv6 addresses prevents it.

- if_lagg(4) now removes IPv6 addresses on a member interfaces
  unconditionally.

- Set reasonable flags to non-IPv6-capable interfaces. [*]

Submitted by:	rpaulo [*]
MFC after:	1 week
Make it so that 'patch < FUBAR' and 'patch -i FUBAR' operate the same.

The former makes a copy of stdin, but was not accurately putting the
content of stdin into a temp file.  This lead to the undercounting
the number of lines in hunks containing NUL characters when reading
from stdin.  Thus resulting in "unexpected end of file in patch" errors.
Properly handle input lines containing NUL characters such that pgets()
accurately fills the read buffer.

Callers of pgets() still mis-process the buffer contents if the read line
contains NUL characters, but this at least makes pgets() accurate.