ss: Fix width calculations when Netid or State columns are missing

ss: Fix width calculations when Netid or State columns are missing

If Netid or State columns are missing, we must not subtract one
for each of these two columns from the remaining screen width,
while distributing available space to columns. This one
character corresponding to one delimiting space has to be
subtracted only if the columns are actually printed.

Further, in the existing implementation, if the screen width is
an odd number, one additional character is added to the width of
one of the two columns.

But if both are not printed, this filling character needs to be
added somewhere else, in order to have the right spacing
allowing us to fill lines completely.

Address and port fields are printed in pairs (local and remote),
so we can't distribute the space to any of them, because it
would be doubled. Instead, print this additional space to the
right of the Send-Q column, to keep code changes to a minimum.

This is particularly visible with 'ss -f netlink -Z'. Before
this patch, with an 80 column terminal, we have:

$ ss -f netlink -Z|head -n3
Recv-Q Send-Q Local Address:Port                 Peer Address:Port
0      0            rtnl:evolution-calen/2049           *                     pr
oc_ctx=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
0      0            rtnl:clock-applet/1944              *                     pr
oc_ctx=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

and with an 81 column terminal:

$ ss -f netlink -Z|head -n3
Recv-Q Send-Q Local Address:Port                 Peer Address:Port
0      0            rtnl:evolution-calen/2049           *                     pro
c_ctx=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
0      0            rtnl:clock-applet/1944              *                     pro
c_ctx=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

After this patch, in both cases, the output is:
$ ss -f netlink -Z|head -n3
Recv-Q Send-Q Local Address:Port                 Peer Address:Port
0      0             rtnl:evolution-calen/2049            *
 proc_ctx=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
0      0             rtnl:clock-applet/1944               *
 proc_ctx=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>