Declare variables static where needed.

Global variables that are used only in the module where they are defined
should be set to static. This gives the compiler better understanding of
the vars, we get warnings if they are unused and also they are zeroed on
program start for free.

These variables were found by pglobal tool from pahole. Here are the
results of this patch on 32-bit defconfig:

bloat-o-meter report:

{{{
  add/remove: 0/3 grow/shrink: 0/5 up/down: 0/-1766 (-1766)
  function                                     old     new   delta
  gbox_decrypt8                                196     195      -1
  main                                        6236    6220     -16
  dvbapi_process_input                        2955    2939     -16
  dvbapi_init_listenfd                         297     281     -16
  CHANNEL_CACHE                                 16       -     -16
  S_EMM_FILTER                                  60       -     -60
  cc_check_version                             727     366    -361
  cwcache                                     1280       -   -1280
}}}

size report:

{{{
    text     data      bss      dec    hex filename
 1000586     1944    60744  1063274 10396a before/oscam-1.20-unstable_svn8488-i486-slackware-linux.debug
 1000406     1760    59336  1061502 10327e  after/oscam-1.20-unstable_svn8489-i486-slackware-linux.debug
}}}

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8489 4b0bc96b-bc66-0410-9d44-ebda105a78c1