ct expr: protocol context updates and dynamic typing

ct expr: protocol context updates and dynamic typing

Include the protocols defined through relational ct expressions in the
protocol context and use the protocol context to dynamically determine
the types of network and transport layer ct expression types.

Before:

$ nft filter output ct proto-dst ssh
<cmdline>:1:28-30: Error: Can't parse symbolic invalid expressions
filter output ct proto-dst ssh
                           ^^^
$ nft filter output ip protocol tcp ct proto-dst ssh
<cmdline>:1:44-46: Error: Can't parse symbolic invalid expressions
filter output ip protocol tcp ct proto-dst ssh
                                           ^^^
$ nft filter output ct protocol tcp ct proto-dst ssh
<cmdline>:1:44-46: Error: Can't parse symbolic invalid expressions
filter output ct protocol tcp ct proto-dst ssh
                                           ^^^
After:

$ nft filter output ct proto-dst ssh
<cmdline>:1:28-30: Error: Can't parse symbolic invalid expressions
filter output ct proto-dst ssh
                           ^^^
$ nft filter output ip protocol tcp ct proto-dst ssh
$ nft filter output ct protocol tcp ct proto-dst ssh

Signed-off-by: Patrick McHardy <kaber@trash.net>