netfilter: Use pr_cont where appropriate

Logging output was changed when simple printks without KERN_CONT
are now emitted on a new line and KERN_CONT is required to continue
lines so use pr_cont.

Miscellanea:

o realign arguments
o use print_hex_dump instead of a local variant

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>