Make NDC not block forever and handle restart.

Still possible for netd to get wedged but system won't die because of it.
Leads the way to having forking netd - then only individual commands would
wedge, promoting stability.

bug:5864209
bug:6019952
Change-Id: I43e4c5072863b8b812d4fe24d30d92eb1a11651a
2 files changed