pppd: Fix printing call in print_option()

print_option() was in this case passing p/opt->addr2 as the format string
instead of the string to be printed (as a quoted string). That could lead
to a nasty crash.

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>