Only update mPipe stats occasionally around the packet loop.

Check for termination or stats update only once every 10,000 times
around the mPipe packet processing loop, to reduce locking.
icmpv6: Fix Coverity warnings on ND_* types

This patch fixes:
** CID 1187544:  Missing break in switch  (MISSING_BREAK)
/src/decode-icmpv6.c: 268 in DecodeICMPV6()

** CID 1187545:  Missing break in switch  (MISSING_BREAK)
/src/decode-icmpv6.c: 270 in DecodeICMPV6()

** CID 1187546:  Missing break in switch  (MISSING_BREAK)
/src/decode-icmpv6.c: 272 in DecodeICMPV6()

** CID 1187547:  Missing break in switch  (MISSING_BREAK)
/src/decode-icmpv6.c: 274 in DecodeICMPV6()

It duplicates the logic instead of adding 'fall through' statements
as the debug statements were wrong and confusing. For ND_REDIRECT
all 5 ND_* types would have been printed.
commandline parsing: check optarg ptr before using it

Fixes:
** CID 1075221:  Dereference after null check  (FORWARD_NULL)
/src/suricata.c: 1344 in ParseCommandLine()

The reason it gave this warning is that in other paths using optarg
there was a check, so the checker assumed optarg can be NULL.