modprobe: use hash table. speeds up significantly if modprobe.dep is large

modprobe: use hash table. speeds up significantly if modprobe.dep is large

function                                             old     new   delta
helper_get_module                                    106     157     +51
config_file_action                                   413     431     +18
modprobe_main                                        690     706     +16
do_modprobe                                          580     588      +8
add_probe                                             81      83      +2
load_modules_dep                                     192     190      -2
get_or_add_modentry                                   10       -     -10
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 5/1 up/down: 95/-12)             Total: 83 bytes

Signed-off-by: Timo Teras <timo.teras@iki.fi>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>