uipc_domain.c : use constant instead of value

[Denis Fondras]

Cosmetic change.

Index: uipc_domain.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_domain.c,v
retrieving revision 1.55
diff -u -p -r1.55 uipc_domain.c
--- uipc_domain.c       23 Nov 2017 13:45:46 -0000      1.55
+++ uipc_domain.c       23 Jun 2018 13:48:51 -0000
@@ -141,7 +141,7 @@ pffindproto(int family, int protocol, in
        const struct protosw *pr;
        const struct protosw *maybe = NULL;
 
-       if (family == 0)
+       if (family == PF_UNSPEC)
                return (NULL);
 
        dp = pffinddomain(family);
@@ -176,7 +176,7 @@ net_sysctl(int *name, u_int namelen, voi
                return (EISDIR);                /* overloaded */
        family = name[0];
 
-       if (family == 0)
+       if (family == PF_UNSPEC)
                return (0);
 #if NBPFILTER > 0
        if (family == PF_BPF)