Below patch cleans the mkiss driver.  After the previous cleanup in
2.4.0-prerelease various code had become unreachable because nothing
was ever setting MKISS_DRIVER_MAGIC.  This fixes fixes an oops - the
mkiss pointer was potencially NULL.  And it also removes the
MOD_{INC,DEC}_USE_COUNT calls.

Alan, lemme know if you want me to cook a 2.4 patch also.

Patch from Jeroen Vreeken PE1RXQ.

Ralf