ofp-print: ofp_packet_to_string() Do not emit extra trailing newline

ofp-print: ofp_packet_to_string() Do not emit extra trailing newline

The string produced by ofp_packet_to_string() includes a trailing
newline, so in the case where packet data is formatted by
ofp_print_packet_out() there is already a newline present.

This patch updates ofp_print_packet_out() so that it does not
add a second newline in this case.

It is not necessary to update the case where there is packet data
to ensure that the result it is terminated by a "\n" as the higher-level
ofp_to_string() function will ensure that the result is "\n" terminated.

The test-suite has be updated to exercise output of packet data by
ofp_packet_to_string()

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>