msm: ipa: teth_bridge: bug fix in get_aggr_capabilities ioctl

Incorrect input validation may cause a kernel memory disclosure to user
space. This fix adds the correct input validation.

Change-Id: Ia0a3f6bae3c9efc48136bad9974516929e76f4fb
CRs-Fixed: 555453
Signed-off-by: Gidon Studinski <gidons@codeaurora.org>