lib: Fixup strlcat and strlcpy to be a bit more descriptive

lib: Fixup strlcat and strlcpy to be a bit more descriptive

When I use these functions and am programming on linux I
always have to pull up a man page for these two functions
since they exist in *BSD land only.

Modify the name of the size variable to destsize on
pass in to give me the small hint I need to know
what to do.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>