Hack: net: PPPoPNS and PPPoLAC build fixes for 4.1

Upstream commit c0371da6 "put iov_iter into msghdr",
added iov_iter and removed direct access to scatter/gather
array elements in msghdr. It broke PPPoLAC and PPPoPNS.

Lets restore the direct access to scatter/gather array in
msghdr for the time being. Otherwise we run into following
build failure:
----------
drivers/net/ppp/pppolac.c: In function ‘pppolac_xmit_core’:
drivers/net/ppp/pppolac.c:210:4: error: unknown field ‘msg_iov’ specified in initializer
    .msg_iov = (struct iovec *)&iov,
    ^
drivers/net/ppp/pppolac.c:211:4: error: unknown field ‘msg_iovlen’ specified in initializer
    .msg_iovlen = 1,
    ^
make[3]: *** [drivers/net/ppp/pppolac.o] Error 1
----------

Change-Id: I2a1245a156da6d93b49f5cfd10506381b0eff005
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>