Update default value of KEY_PREFERRED_IKE_PROTOCOL_INT

Some carriers' networks not support IPv6 very well. The existing
default value(0) will use IPv6 if networks support IPv6. Update
the default value to an invalid value so that the code that uses
the key could tell and fall into a reasonable case.

Bug: 269714970
Bug: 284246686
Test: m ; flash and check the value
(cherry picked from https://android-review.googlesource.com/q/commit:437f84c62671ba30ae62cb21a28be2323d671ad1)
Merged-In: Ie2b42e69702609b132acd6bd087292bf9df365cb
Change-Id: Ie2b42e69702609b132acd6bd087292bf9df365cb