nbd-client: support newstyle protocol, -b, -d, -p, -N

nbd-client: support newstyle protocol, -b, -d, -p, -N

Recognize the "newstyle" protocol and switch to it automatically.
Add options for setting blocksize (-b) and for disconnecting
a nbd device (-d).

function                                             old     new   delta
nbdclient_main                                       492    1179    +687
static.long_options                                    -      80     +80
print_direc                                          438     457     +19
brctl_main                                          1169    1183     +14
bb_strtoll                                            84      89      +5
packed_usage                                       33082   33066     -16
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/1 up/down: 805/-16)           Total: 789 bytes

Signed-off-by: Elvira Khabirova <lineprinter@altlinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>