Document pffinddomain().

Reviewed by:	glebius

share/man/man9/Makefile

@@ -620,6 +620,7 @@ MLINKS+=domain.9 DOMAIN_SET.9 \
 	domain.9 domain_add.9 \
 	domain.9 pfctlinput.9 \
 	domain.9 pfctlinput2.9 \
+	domain.9 pffinddomain.9 \
 	domain.9 pffindproto.9 \
 	domain.9 pffindtype.9
 MLINKS+=drbr.9 drbr_free.9 \

share/man/man9/domain.9

@@ -26,13 +26,14 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 5, 2012
+.Dd December 7, 2012
 .Dt DOMAIN 9
 .Os
 .Sh NAME
 .Nm domain_add ,
 .Nm pfctlinput ,
 .Nm pfctlinput2 ,
+.Nm pffinddomain ,
 .Nm pffindproto ,
 .Nm pffindtype ,
 .Nm DOMAIN_SET
@@ -48,6 +49,8 @@
 .Fn pfctlinput "int cmd" "struct sockaddr *sa"
 .Ft void
 .Fn pfctlinput2 "int cmd" "struct sockaddr *sa" "void *ctlparam"
+.Ft struct domain *
+.Fn pffinddomain "int family"
 .Ft struct protosw *
 .Fn pffindproto "int family" "int protocol" "int type"
 .Ft struct protosw *
@@ -176,6 +179,12 @@ This is because there is
 no reference counting system in place to determine if there are any
 active references from sockets within that domain.
 .Pp
+.Fn pffinddomain
+finds a domain by family.
+If the domain cannot be found,
+.Dv NULL
+is returned.
+.Pp
 .Fn pffindtype
 and
 .Fn pffindproto