HPCC-12128 - MP connections take too long

Resolve mp connection deadlock when A->B and B->A with lower random number

Signed-off-by: Mark Kelly <mark.kelly@lexisnexis.com>
See comments re. need for attachsect (given it looks like it's already always thread safe as in connectsect), if so, then no need for attachchk to be an atomic either.