ip: Fix crash in ip address add on sub-int without exact-match

Type: fix

Creating a sub-int without exact-match set, and subsequently adding an
IPv4 or IPv6 address will crash VPP. This fix catches this situation and
refuses to allow the caller to add an IPv4 or IPv6 address on an
ethernet sub-int that does not have exact-match set.

TESTED:
Before this change, the following crashes VPP:

```
DBGvpp# cre sub TenGigabitEthernet3/0/0 1 dot1q 10
TenGigabitEthernet3/0/0.1
DBGvpp# set interface ip address TenGigabitEthernet3/0/0.1 2001:db8::1/64
<crash>
```

After the change, VPP refuses to act:

```
DBGvpp# cre sub TenGigabitEthernet3/0/0 1 dot1q 10
TenGigabitEthernet3/0/0.1
DBGvpp# set interface ip address TenGigabitEthernet3/0/0.1 192.0.2.1/30
set interface ip address: sub-interface without exact-match doesn't support IP addressing
DBGvpp# set interface ip address TenGigabitEthernet3/0/0.1 2001:db8:1/64
set interface ip address: sub-interface without exact-match doesn't support IP addressing
```

Signed-off-by: Pim van Pelt <pim@ipng.nl>
Change-Id: I42997db314225cd186ebb54013b5717ace7f7bd6