wifi: ignore SIGPIPE when dumping stats to dumpstate

If dumpstate closes the reading end of the pipe (likely due to timeout)
and wifi vendor hal attempts to write to the fd it received from
dumpstate, it will receive sig 13 (SIGPIPE), and is then killed.
We should protect wifi vendor hal from the abnormally behaved clients.

Sync patch from ag/12321138. Reference from b/172972545 &
b/161336019#comment29

Bug: 161336019
Bug: 172972545
Test: Manuel Test, Wifi works normally
Change-Id: Ie7de040ac4320f83500c18e74e3c58d63b4df1b7