first fruits - kill l2cap ->memcpy_fromiovec()

Just use copy_from_iter().  That's what this method is trying to do
in all cases, in a very convoluted fashion.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc include/net/bluetooth/l2cap.h
Simple merge

diff --cc net/bluetooth/6lowpan.c
Simple merge

diff --cc net/bluetooth/a2mp.c
Simple merge

diff --cc net/bluetooth/l2cap_core.c
Simple merge

diff --cc net/bluetooth/l2cap_sock.c
Simple merge

diff --cc net/bluetooth/smp.c
Simple merge