Tell libpcap that we have strlcpy.

Without this, libpcap ends up defining strlcpy as a macro before it
ever includes string.h. It then includes string.h, and ends up
rewriting the function decl with the macro body, breaking the build.

Test: mma
Bug: None
Change-Id: I677e4ac8ac002ab80c2ba478cf2dfa9da2e0cfc3