net/sfc: improve naming in flow tunnel offload support

net/sfc: improve naming in flow tunnel offload support

Change ambiguous terms "jump rule" and "group rule" to
clearer "tunnel rule" and "switch rule". The new terms
reflect the purpose of these rules in virtual switches.

The module name, "flow tunnel", is replaced by "FT" in
function names to avoid the use of word "tunnel" twice.

Use term "FT context" when referring to tunnel entries.
Also, add "ctx" suffix to "ft" and "ft_id" occurrences.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>