net-mgmt/net-snmp: compile error: error: variable has incomplete type 'struct ifaddr' struct ifaddr ifaddr;

[O. Hartmann]

Portnet-mgmt/net-snmp fails to update/build on CURRENT:

libtool: compile:  cc -I../../include -I. -I../../agent
-I../../agent/mibgroup -I../../snmplib -I/usr/include
-DNETSNMP_ENABLE_IPV6 -fno-strict-aliasing -O2 -pipe -O3 -march=native
-I/usr/local/include -I/include -D_WANT_IFADDR -fstack-protector
-fno-strict-aliasing -std=c99 -Ufreebsd11 -Dfreebsd11=freebsd11
-DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -fno-strict-aliasing -pipe
-fstack-protector -I/usr/local/include
-I/usr/local/lib/perl5/5.18/mach/CORE -c mibII/ipv6.c  -fPIC -DPIC -o
mibII/.libs/ipv6.o mibII/ipv6.c:806:20: warning: returning 'char *'
from a function with result type 'u_char *' (aka 'unsigned char *')
converts between pointers to integer types with different sign
[-Wpointer-sign] return p; ^ mibII/ipv6.c:848:29: error: variable has
incomplete type 'struct ifaddr' struct ifaddr   ifaddr;