udhcpc: fix BPF filter. Hopefully fixes the root cause of 4598 and 6746

Use a *signed* large positive value in BPF filter to indicate success.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Kbuild: move CONFIG_PAM to general configuration

Currently CONFIG_PAM depends on CONFIG_LOGIN, but is used by the httpd applet too.

This patch moves said option to general configuration, thus allowing to
compile httpd with PAM support independently from login.

Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>