ip rule: fix clang warning.

ip rule: fix clang warning.

```
[2/1209] Compiling C object 'src/network/src@network@@networkd-core@sta/networkd-routing-policy-rule.c.o'.
FAILED: src/network/src@network@@networkd-core@sta/networkd-routing-policy-rule.c.o
clang -Isrc/network/src@network@@networkd-core@sta -Isrc/network -I../src/network -Isrc/basic -I../src/basic -Isrc/shared -I../src/shared -Isrc/systemd -I../src/systemd -Isrc/journal -I../src/journal -Isrc/journal-remote -I../src/journal-remote -Isrc/nspawn -I../src/nspawn -Isrc/resolve -I../src/resolve -Isrc/timesync -I../src/timesync -I../src/time-wait-sync -Isrc/login -I../src/login -Isrc/udev -I../src/udev -Isrc/libudev -I../src/libudev -Isrc/core -I../src/core -I../src/libsystemd/sd-bus -I../src/libsystemd/sd-device -I../src/libsystemd/sd-event -I../src/libsystemd/sd-hwdb -I../src/libsystemd/sd-id128 -I../src/libsystemd/sd-netlink -I../src/libsystemd/sd-network -Isrc/libsystemd-network -I../src/libsystemd-network -I. -I../ -Xclang -fcolor-diagnostics -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Werror -std=gnu99 -O0 -g -Wextra -Werror=undef -Wmissing-include-dirs -Wold-style-definition -Wpointer-arith -Winit-self -Wfloat-equal -Werror=missing-prototypes -Werror=implicit-function-declaration -Werror=missing-declarations -Werror=return-type -Werror=incompatible-pointer-types -Werror=format=2 -Wstrict-prototypes -Wredundant-decls -Wmissing-noreturn -Wshadow -Wendif-labels -Wstrict-aliasing=2 -Wwrite-strings -Werror=overflow -Werror=shift-count-overflow -Wdate-time -Wnested-externs -Wno-unused-parameter -Wno-missing-field-initializers -Wno-unused-result -Wno-error=nonnull -ffast-math -fno-common -fdiagnostics-show-option -fno-strict-aliasing -fvisibility=hidden -fstack-protector -fstack-protector-strong --param=ssp-buffer-size=4 -fPIE -Wno-typedef-redefinition -Wno-gnu-variable-sized-type-not-at-end -Werror=shadow -include config.h -fPIC  -MD -MQ 'src/network/src@network@@networkd-core@sta/networkd-routing-policy-rule.c.o' -MF 'src/network/src@network@@networkd-core@sta/networkd-routing-policy-rule.c.o.d' -o 'src/network/src@network@@networkd-core@sta/networkd-routing-policy-rule.c.o' -c ../src/network/networkd-routing-policy-rule.c
../src/network/networkd-routing-policy-rule.c:1071:33: error: format specifies type 'unsigned char' but the argument has type '__u16' (aka 'unsigned short') [-Werror,-Wformat]
                                rule->sport.start, rule->sport.end);
                                ^~~~~~~~~~~~~~~~~
../src/network/networkd-routing-policy-rule.c:1071:52: error: format specifies type 'unsigned char' but the argument has type '__u16' (aka 'unsigned short') [-Werror,-Wformat]
                                rule->sport.start, rule->sport.end);
                                                   ^~~~~~~~~~~~~~~
../src/network/networkd-routing-policy-rule.c:1078:33: error: format specifies type 'unsigned char' but the argument has type '__u16' (aka 'unsigned short') [-Werror,-Wformat]
                                rule->dport.start, rule->dport.end);
                                ^~~~~~~~~~~~~~~~~
../src/network/networkd-routing-policy-rule.c:1078:52: error: format specifies type 'unsigned char' but the argument has type '__u16' (aka 'unsigned short') [-Werror,-Wformat]
                                rule->dport.start, rule->dport.end);
                                                   ^~~~~~~~~~~~~~~
4 errors generated.
```