main/pbx: Resolve case sensitivity regression in PBX hints

When 8297136f was merged for ASTERISK-25040, a regression was introduced
surrounding the case sensitivity of device names within hints.
Previously, device names - such as 'sip/foo' - were compared in a case
insensitive fashion. Thus, 'sip/foo' was equivalent to 'SIP/foo'. After
that patch, only the case sensitive name would match, i.e., 'SIP/foo'.
As a result, some dialplan hints stopped working.

This patch re-introduces case insensitive matching for device names in
hints.

ASTERISK-25040

ASTERISK-25202 #close

Change-Id: If5046a7d14097e1e3c12b63092b9584bb1e9cb4c