net: hdlc: rename 'mod_init' & 'mod_exit' functions to be module-specific

Rename module_init & module_exit functions that are named
"mod_init" and "mod_exit" so that they are unique in both the
System.map file and in initcall_debug output instead of showing
up as almost anonymous "mod_init".

This is helpful for debugging and in determining how long certain
module_init calls take to execute.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Martin Schiller <ms@dev.tdt.de>
Cc: linux-x25@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>