odhcp6c: sync and accumulate RA & DHCPv6 events as fast as possible

[alinnastac]

This fixes dc186d6d2b0dd4ad23ca5fc69c00e81f796ff6d9 commit which introduce accumulation delay differences between the 2 possible scenarios:

1. When DHCPv6 bound event precede RA receival, sync script is called after 1 second since accumulation has been completed (i.e. RA has been received).
2. When RA receival precedes DHCPv6 bound event, sync script is called after a delay of 10 seconds since accumulation is done.