Don't insert newline in -o (oneline) mode; print mark as hex.

Oneline mode is supposed to force all output to be on oneline and
machine-parsable, but this isn't the case for "ip xfrm" as shown:

% ip -o xfrm monitor
...
src 0.0.0.0/0 dst 0.0.0.0/0 \   dir out priority 2051 ptype main \  mark -1879048191/0xffffffff
    tmpl src 203.0.130.10 dst 198.51.130.30\        proto esp reqid 16384 mode tunnel\
...

as that's 2 lines, not one. Also, the "mark" is shown in signed
decimal, but the mask is in hex. This is confusing: let's use
hex for both.
Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>