ipvs: ip_vs_proto: local functions should not be exposed globally

Functions not referenced outside of a source file should be marked
static to prevent it from being exposed globally.

This quiets the sparse warnings:

warning: symbol '__ipvs_proto_data_get' was not declared. Should it be static?

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Simon Horman <horms@verge.net.au>