[NET]: Accept wildcard delimiters in in[46]_pton

Accept -1 as delimiter to abort parsing without an error at the first
unknown character. This is needed by the upcoming nf_conntrack SIP
helper, where addresses are delimited by either '\r' or '\n' characters.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>