msm: ipa: update stub functions

When CONFIG_RNDIS_IPA is disabled the stub functions cause
compilation errors. Make the offending stub functions static
and inline to fix the issue

CRs-fixed: 1058461
Change-Id: Id7cb088eae5dfd9f19338eaf7690a7f5aec10e09
Signed-off-by: Clyde Byrd III <cbyrd@codeaurora.org>