Updated documentation indicates that four WEP key values must be
provided. This replaces the earlier reference to "up to four." Providing
fewer than four values causes a java.lang.IllegalArgumentException.
Documentation also references the option to provide empty strings for up
to three of the values.
Test: make ds-docs
Bug: 36949880
Change-Id: I1da9f0ecfb390623f4d53ca508a554303861ed98
Exempt-From-Owner-Approval: Docs-only change
f0d5c5c30a