net/llc/llc_conn.c: fix 4 instances of -Wmissing-variable-declarations

I'm looking to enable -Wmissing-variable-declarations behind W=1. 0day
bot spotted the following instances:

  net/llc/llc_conn.c:44:5: warning: no previous extern declaration for
  non-static variable 'sysctl_llc2_ack_timeout'
  [-Wmissing-variable-declarations]
  44 | int sysctl_llc2_ack_timeout = LLC2_ACK_TIME * HZ;
     |     ^
  net/llc/llc_conn.c:44:1: note: declare 'static' if the variable is not
  intended to be used outside of this translation unit
  44 | int sysctl_llc2_ack_timeout = LLC2_ACK_TIME * HZ;
     | ^
  net/llc/llc_conn.c:45:5: warning: no previous extern declaration for
  non-static variable 'sysctl_llc2_p_timeout'
  [-Wmissing-variable-declarations]
  45 | int sysctl_llc2_p_timeout = LLC2_P_TIME * HZ;
     |     ^
  net/llc/llc_conn.c:45:1: note: declare 'static' if the variable is not
  intended to be used outside of this translation unit
  45 | int sysctl_llc2_p_timeout = LLC2_P_TIME * HZ;
     | ^
  net/llc/llc_conn.c:46:5: warning: no previous extern declaration for
  non-static variable 'sysctl_llc2_rej_timeout'
  [-Wmissing-variable-declarations]
  46 | int sysctl_llc2_rej_timeout = LLC2_REJ_TIME * HZ;
     |     ^
  net/llc/llc_conn.c:46:1: note: declare 'static' if the variable is not
  intended to be used outside of this translation unit
  46 | int sysctl_llc2_rej_timeout = LLC2_REJ_TIME * HZ;
     | ^
  net/llc/llc_conn.c:47:5: warning: no previous extern declaration for
  non-static variable 'sysctl_llc2_busy_timeout'
  [-Wmissing-variable-declarations]
  47 | int sysctl_llc2_busy_timeout = LLC2_BUSY_TIME * HZ;
     |     ^
  net/llc/llc_conn.c:47:1: note: declare 'static' if the variable is not
  intended to be used outside of this translation unit
  47 | int sysctl_llc2_busy_timeout = LLC2_BUSY_TIME * HZ;
     | ^

These symbols are referenced by more than one translation unit, so make
include the correct header for their declarations. Finally, sort the
list of includes to help keep them tidy.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/llvm/202308081000.tTL1ElTr-lkp@intel.com/
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230808-llc_static-v1-1-c140c4c297e4@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>