The refactoring done in commit d181d14b "slirp: use a dedicated field
for chardev pointer" forgot to change one place in slirp_state_load
where 'ex_exec' was used to store the chardev ptr. This broke loading
of saved state.

Later commit 4f38cfb5 "slirp: remove unused EMU_RSH" removed this line
all together, as it now looked like it didn't do anything.

This commit ensures that guestfwd is properly setup on the socket when
loading state.

Signed-off-by: Anders Waldenborg <anders@0x63.nu>