net: pktgen: Fix interface flags printing

Device flags are displayed incorrectly:
1) The comparison (i == F_FLOW_SEQ) is always false, because F_FLOW_SEQ
is equal to (1 << FLOW_SEQ_SHIFT) == 2048, and the maximum value
of the 'i' variable is (NR_PKT_FLAG - 1) == 17. It should be compared
with FLOW_SEQ_SHIFT.

2) Similarly to the F_IPSEC flag.

3) Also add spaces to the print end of the string literal "spi:%u"
to prevent the output from merging with the flag that follows.

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with SVACE.

Fixes: 99c6d3d2

 ("pktgen: Remove brute-force printing of flags")
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@infotecs.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>