TXT records: fix parsing records with whitespace (e.g. ty=)
TXT records: fix parsing records with whitespace (e.g. ty=)

My printer sets ty=Brother MFC-L2750DW series, which was previously cut off:

2020/07/18 17:14:40 DNSSD service discovered: {Brother\ MFC-L2750DW\ series
_uscan._tcp local BRNaaaaaaaaaaaa map[cs:binary,grayscale,color duplex:T
is:adf,platen note: pdl:application/pdf,image/jpeg rs:eSCL txtvers:1 ty:Brother
vers:2.63] 1h15m0s 80 [10.0.0.230]

But with this change, the record is parsed correctly:

2020/07/18 17:22:58 DNSSD service discovered: {Brother\ MFC-L2750DW\ series
_uscan._tcp local BRNaaaaaaaaaaaa map[cs:binary,grayscale,color duplex:T
is:adf,platen note: pdl:application/pdf,image/jpeg rs:eSCL txtvers:1 ty:Brother
MFC-L2750DW series vers:2.63] 1h15m0s 80 [10.0.0.230]

The format is described in more detail in RFC 6763 section 6:
https://tools.ietf.org/html/rfc6763#section-6

Notably, there is no whitespace-based framing specified, so I think the previous
code was just a mistake or misunderstanding.

brutella/dnssd